The role of episodic overturn in generating the surface geology and heat flow on Enceladus
Craig O’|Neill & Francis Nimmo 2010, Nature Geoscience 3, 88–91
http://www.nature.com/ngeo/journal/v3/n2/full/ngeo731.html
Enceladus, Saturn’s second closest satellite, is well known for its icy and even snowy aspect and structure. It has a diameter of 500km and, even though it is all composed out of ice, it has shown signs of tectonic and volcanic activity, which, interestingly, is concentrated in the south pole of the moon, emanating geyserlike jets, watery plumes that spew outward from a region carved up by unusually warm gashes known as "tiger stripes"
O’Neill & Nimmo 2010 observed abnormally high heat flux at the south pole which can be explained by the existence of a convecting mantle plume under the moon’s tectonic plates. They propose a model through which this dispersion can very probably be due to tidal heating. This effect could be possible in the south pole due to the ice shell being thinner over a region with a warmer interior.
During Enceladus orbit around Saturn, the strong gravity from the massive planet causes the icy moon to “stretch”, thus generating tidal heat waves (similar to the tidal waves on Earth cause by the moon). O'Neill & Nimmo 2010 assume that what is being observed on Enceladus currently is quite an unusual behavior which can be described as a brief period of tectonic activity that resurfaces a limited area of the moon. In the model that they create, they describe how the heat is being stored up inside over billions of years, thus, building up to a maximum point at which it starts “erupting, escaping in a brief volcanic-like activity.
Friday, March 5, 2010
Article Summary #14
Saturn's largest ring
A. J. Verbiscer, M. F. Skrutskie, D. P. Hamilton, 2009, Nature 461, 1098-1100
http://www.nature.com/nature/journal/v461/n7267/full/nature08515.html
By analyzing data from the Spitzer Space Telescope’s MIPS (multi-band imaging photometer), Verbiscer et al. 2009 conducted an investigation on one of Saturn’s satellites, Phoebe, in order to look for a broad debris disk. A debris disk is a circumstellar disk of dust and debris in orbit around a star and can constitute a phase in the formation of a planetary system following the protoplanetary disk phase.
By looking at mid-infrared images of Saturn’s ecliptic plane, Verbiscer et al. 2009 detected a diffused band of light with two peaks which they knew did not come from the planet’s scattered light.
In most cases, the moon of a planet continuously supplies dust to a planetary ring associated with it, but this has been observed for the satellites that are closest to their planets. In this paper, Verbiscer et al. 2009 discuss the discovery of a ring of this type for Phoebe. This phenomenon is very unusual because Phoebe is very far from its hosting planet (a distance hundreds of times greater than the radius of Saturn), and the disk appears to be ~40 times thicker than the same radius and matches the satellite’s orbit and its vertical range.
This ring has not been detected before due to the fact that its composed out of particles smaller than 1cm and the impacts on Phoebe are the main material supplement for the ring. Its dispersion, which for other rings is know to be equatorial, was observed as symmetric about Saturn’s plane orbit.
Lastly, Verbiscer et al. 2009 noticed a similarity between Phoebe and its ring: they have retrograde orbits which are different from other moon-ring systems with a counter-clockwise orbit.
A. J. Verbiscer, M. F. Skrutskie, D. P. Hamilton, 2009, Nature 461, 1098-1100
http://www.nature.com/nature/journal/v461/n7267/full/nature08515.html
By analyzing data from the Spitzer Space Telescope’s MIPS (multi-band imaging photometer), Verbiscer et al. 2009 conducted an investigation on one of Saturn’s satellites, Phoebe, in order to look for a broad debris disk. A debris disk is a circumstellar disk of dust and debris in orbit around a star and can constitute a phase in the formation of a planetary system following the protoplanetary disk phase.
By looking at mid-infrared images of Saturn’s ecliptic plane, Verbiscer et al. 2009 detected a diffused band of light with two peaks which they knew did not come from the planet’s scattered light.
In most cases, the moon of a planet continuously supplies dust to a planetary ring associated with it, but this has been observed for the satellites that are closest to their planets. In this paper, Verbiscer et al. 2009 discuss the discovery of a ring of this type for Phoebe. This phenomenon is very unusual because Phoebe is very far from its hosting planet (a distance hundreds of times greater than the radius of Saturn), and the disk appears to be ~40 times thicker than the same radius and matches the satellite’s orbit and its vertical range.
This ring has not been detected before due to the fact that its composed out of particles smaller than 1cm and the impacts on Phoebe are the main material supplement for the ring. Its dispersion, which for other rings is know to be equatorial, was observed as symmetric about Saturn’s plane orbit.
Lastly, Verbiscer et al. 2009 noticed a similarity between Phoebe and its ring: they have retrograde orbits which are different from other moon-ring systems with a counter-clockwise orbit.
Article Summary #13
A single sub-kilometre Kuiper belt object from a stellar occultation in archival data
H. E. Schlichting, E. O. Ofek, M. Wenz et al. 2009, Nature, 462, 895
http://www.nature.com/nature/journal/v462/n7275/full/nature08608.html
In our Solar System one remnant from its early evolutionary state is the Kuiper belt, a flow of material found beyond Neptune that orbits the Sun. For this system, size distribution is crucial because it can give information about the physical history of the Kuiper belt and the objects that it consists of.
Because the Kuiper belt is located so far from the Earth, the direct detection on small objects (<1km in diameter) is not possible, but they their effects can be observed: they cause occultations which are changes in the light curve due to the object’s obscuration of a star located in the background. The variation cause a diffraction pattern of the radiation emitted by the background star which depends on several factors: the Kuiper belt object’s size and distance, angular size of the star and other additional parameters.
Thus, by looking at the occultations, Schlichting et al. 2009 detected object with a radius of ~500m, located at a distance of ~45AU (astronomical units). The probability of result being a cause of random statistical error is almost zero, which is a strong proof of the accuracy of the detection.
Since out of all the Kuiper belt objects observed so far this event has been unique. Schlichting et al. 2009 believe that there is a deficit of these small Kuiper belt objects in comparison with the ones that have radii bigger than 50km, distribution which can be explained through the fact that the sub-kilometer objects are experiencing erosion through collisions.
H. E. Schlichting, E. O. Ofek, M. Wenz et al. 2009, Nature, 462, 895
http://www.nature.com/nature/journal/v462/n7275/full/nature08608.html
In our Solar System one remnant from its early evolutionary state is the Kuiper belt, a flow of material found beyond Neptune that orbits the Sun. For this system, size distribution is crucial because it can give information about the physical history of the Kuiper belt and the objects that it consists of.
Because the Kuiper belt is located so far from the Earth, the direct detection on small objects (<1km in diameter) is not possible, but they their effects can be observed: they cause occultations which are changes in the light curve due to the object’s obscuration of a star located in the background. The variation cause a diffraction pattern of the radiation emitted by the background star which depends on several factors: the Kuiper belt object’s size and distance, angular size of the star and other additional parameters.
Thus, by looking at the occultations, Schlichting et al. 2009 detected object with a radius of ~500m, located at a distance of ~45AU (astronomical units). The probability of result being a cause of random statistical error is almost zero, which is a strong proof of the accuracy of the detection.
Since out of all the Kuiper belt objects observed so far this event has been unique. Schlichting et al. 2009 believe that there is a deficit of these small Kuiper belt objects in comparison with the ones that have radii bigger than 50km, distribution which can be explained through the fact that the sub-kilometer objects are experiencing erosion through collisions.
Article Summary #12
An Orbital Period of 0.94 days for the Hot Jupiter Planet WASP-18b
C. Hellier, D. R. Anderson, A. Collier Cameron, et al. 2009, Nature, Vol 460, 1098
http://www.nature.com/nature/journal/v460/n7259/full/nature08245.html
“Hot Jupiters” are exoplanets that initially form at the edge of their stellar system, far from their host stars, but due to the interactions with the proto-planetary disk (the disk around a young star consisting of highly dense gas that rotates around it) or by interaction with a massive object (i.e. massive planet), they end up in the star’s proximity (~0.02 astronomical units). Due to this short distance, the radiation from the star increases the planet’s temperature.
Hellier et al. 2009 look at the planet WASP-18b (first exoplanet that was confirmed to have a period smaller than a day) and analyze is tidal interactions with its host star. They found the stellar mass to be close to that of our Sun and the stellar age of 630 Myr, this making it one of the youngest known planet-hosting stars.
Tidal interaction theory states that when a massive planet is close enough to its host star it causes the formation of a “tidal bulge” on that star (similarly to the how the moon causes the formation of water tides on Earth). That bulge exerts a torque on the planet, decreasing the angular momentum of the planet and, thus, the latter starts spiraling inwards towards the star. The time required for the planet to spiral onto the star depends on several characteristics of the planet: mass, orbit, distance, and a tidal dissipation parameter Q (a quality factor that describes the ratio of the available energy to the dissipated energy during each period). This paper discusses how the value of Q affects the planet-star interaction.
The result they found was that if the Q calculated for the Solar System bodies would apply to WASP-18b, then the star would be spiraling inwards onto the host star in a very short time (less than 1% of the lifetime of its host star). Thus, it is assumed that this planet is an exception from what has been seen so far, or that the Q value does not apply to all systems in the same way.s
C. Hellier, D. R. Anderson, A. Collier Cameron, et al. 2009, Nature, Vol 460, 1098
http://www.nature.com/nature/journal/v460/n7259/full/nature08245.html
“Hot Jupiters” are exoplanets that initially form at the edge of their stellar system, far from their host stars, but due to the interactions with the proto-planetary disk (the disk around a young star consisting of highly dense gas that rotates around it) or by interaction with a massive object (i.e. massive planet), they end up in the star’s proximity (~0.02 astronomical units). Due to this short distance, the radiation from the star increases the planet’s temperature.
Hellier et al. 2009 look at the planet WASP-18b (first exoplanet that was confirmed to have a period smaller than a day) and analyze is tidal interactions with its host star. They found the stellar mass to be close to that of our Sun and the stellar age of 630 Myr, this making it one of the youngest known planet-hosting stars.
Tidal interaction theory states that when a massive planet is close enough to its host star it causes the formation of a “tidal bulge” on that star (similarly to the how the moon causes the formation of water tides on Earth). That bulge exerts a torque on the planet, decreasing the angular momentum of the planet and, thus, the latter starts spiraling inwards towards the star. The time required for the planet to spiral onto the star depends on several characteristics of the planet: mass, orbit, distance, and a tidal dissipation parameter Q (a quality factor that describes the ratio of the available energy to the dissipated energy during each period). This paper discusses how the value of Q affects the planet-star interaction.
The result they found was that if the Q calculated for the Solar System bodies would apply to WASP-18b, then the star would be spiraling inwards onto the host star in a very short time (less than 1% of the lifetime of its host star). Thus, it is assumed that this planet is an exception from what has been seen so far, or that the Q value does not apply to all systems in the same way.s
Article Summary #11
Dust emission from a parsec-scale structure in the Seyfert 1 nucleus of NGC 4151
Burtscher, L.; Jaffe, W.; Raban, et al. 2009, D., The Astrophysical Journal Letters, Volume 705, Issue 1, pp. L53-L57
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0909.5191
Active Galactic Nuclei (AGN) are galaxies with an actively accreting supermassive black hole at the center. The main mechanism of the black holes consists of strong material accretion that results in the emission of broad emission lines which we can observe in the spectra (the area where the broad lines are emitted from is called the “broad line region”). This region is believed to be surrounded by a dusty torus which is a “doughnut”-shaped structure, consisting of gas and it is coplanar with the galactic plane.
The galaxies that are oriented “edge-on” relative to our line of sight (i.e. we cannot see the center directly, but we see it through this “doughnut”) are named “Seyfert type 2”, and the galaxies for which we have a direct (“top”) view are called “Seyfert type 1”. The unified model of these types of AGN states that for both type 1 and type 2 the dust distribution should be identical, and the differences observed in the detections should be caused only by the orientation relative to our line of sight. So far, though, there has not been enough supporting evidence for this theory.
The data used consists of observations made with MIDI (mid-infrared interferometric instrument) in the N energy band (radiation wavelengths between 8μm and 13μm) on the galaxy NGC 4151 (the closest Seyfert type 1). With the infrared data, Burtscher et al. 2009 were able to measure the thermal emission from the center of the galaxy.
What was found was that the temperature of the thermal emission and the diameter of the dust emission region are similar to what has been observed in the Seyfert type 2 galaxies. This is important because it is one of the first major findings that support the unification model, although numerous details need deeper analysis for a better understanding.
Burtscher, L.; Jaffe, W.; Raban, et al. 2009, D., The Astrophysical Journal Letters, Volume 705, Issue 1, pp. L53-L57
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0909.5191
Active Galactic Nuclei (AGN) are galaxies with an actively accreting supermassive black hole at the center. The main mechanism of the black holes consists of strong material accretion that results in the emission of broad emission lines which we can observe in the spectra (the area where the broad lines are emitted from is called the “broad line region”). This region is believed to be surrounded by a dusty torus which is a “doughnut”-shaped structure, consisting of gas and it is coplanar with the galactic plane.
The galaxies that are oriented “edge-on” relative to our line of sight (i.e. we cannot see the center directly, but we see it through this “doughnut”) are named “Seyfert type 2”, and the galaxies for which we have a direct (“top”) view are called “Seyfert type 1”. The unified model of these types of AGN states that for both type 1 and type 2 the dust distribution should be identical, and the differences observed in the detections should be caused only by the orientation relative to our line of sight. So far, though, there has not been enough supporting evidence for this theory.
The data used consists of observations made with MIDI (mid-infrared interferometric instrument) in the N energy band (radiation wavelengths between 8μm and 13μm) on the galaxy NGC 4151 (the closest Seyfert type 1). With the infrared data, Burtscher et al. 2009 were able to measure the thermal emission from the center of the galaxy.
What was found was that the temperature of the thermal emission and the diameter of the dust emission region are similar to what has been observed in the Seyfert type 2 galaxies. This is important because it is one of the first major findings that support the unification model, although numerous details need deeper analysis for a better understanding.
Article Summary #10
Dark matter haloes determine the masses of supermassive black holes
C. M. Booth, Joop Schaye, 2009, eprint arXiv:0911.0935
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0911.0935
Suppermassive Black Holes (SMBH) are found in the center of most massive galaxies and the characteristics of the black holes are known to be strongly related to its host galaxy.
Black holes, as described by general relativity, are a region of space from which nothing can escape, not even light. It is a very compact and massive object that is know to deform space and time and they receive their mass through the accretion of matter around them. The material accelerates during its fall into the black hole, becomes hotter and starts radiating in various energy ranges (depending on its temperature). This radiated energy is what causes the correlation between the black hole’s properties and those of the Galaxy.
It has bee discovered that SMBH are always gravitationally dominant and this is thought to be due to its ability to regulate the rate at which it accretes the matter around it (this phenomenon is called “self-regulation”). The luminous center of the galaxy is called the “bulge” and it is not clear whether the self-regulation occurs inside the bulge (i.e. <1 kpc), on the galaxy scale, or in the entire dark matter halo around the galaxy.
Their analysis is done through a simulation of a black hole and its host galaxy. The goal is finding the initial conditions that would result in a black hole-galaxy evolution to the current state and correlations observed. What was found was unexpected: the energy transferred from the black hole into the surrounding medium does not change when the fraction of the accreted rest mass energy is increased. Also, another result from the simulations is that it is not the stellar mass in the galaxy, but rather the mass of the dark matter halo that determines the mass of the black hole.
C. M. Booth, Joop Schaye, 2009, eprint arXiv:0911.0935
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0911.0935
Suppermassive Black Holes (SMBH) are found in the center of most massive galaxies and the characteristics of the black holes are known to be strongly related to its host galaxy.
Black holes, as described by general relativity, are a region of space from which nothing can escape, not even light. It is a very compact and massive object that is know to deform space and time and they receive their mass through the accretion of matter around them. The material accelerates during its fall into the black hole, becomes hotter and starts radiating in various energy ranges (depending on its temperature). This radiated energy is what causes the correlation between the black hole’s properties and those of the Galaxy.
It has bee discovered that SMBH are always gravitationally dominant and this is thought to be due to its ability to regulate the rate at which it accretes the matter around it (this phenomenon is called “self-regulation”). The luminous center of the galaxy is called the “bulge” and it is not clear whether the self-regulation occurs inside the bulge (i.e. <1 kpc), on the galaxy scale, or in the entire dark matter halo around the galaxy.
Their analysis is done through a simulation of a black hole and its host galaxy. The goal is finding the initial conditions that would result in a black hole-galaxy evolution to the current state and correlations observed. What was found was unexpected: the energy transferred from the black hole into the surrounding medium does not change when the fraction of the accreted rest mass energy is increased. Also, another result from the simulations is that it is not the stellar mass in the galaxy, but rather the mass of the dark matter halo that determines the mass of the black hole.
Article Summary #9
Measuring the Cosmic-Ray Acceleration Efficiency of a Supernova Remnant
E. A. Helder, J. Vink, C. G. Bassa, A. Bamba, et al. 2009, Science, 325, 719
http://www.sciencemag.org/cgi/content/abstract/325/5941/719
A widely studied topic both by astronomers and physicist today is Cosmic Rays, which are highly energetic particles that originate outside the Earth, travel through the universe, and hit our atmosphere. A known sub-category is that of accelerated cosmic rays and the accelerating process behind it is know to be mostly due to supernova remnants (SNR – expanding plasma shells caused by strong and violent exploding stars into supernovae and its boundary is called a “shock wave”) . This paper discusses one scenario of how a supernova remnant can accelerate the cosmic rays.
It has been found that for the known cosmic ray density to be stable in the Milky Way, every century three supernovae transform a tenth of their kinetic energy in cosmic ray energy. Supernova remnants lose a high amount of energy to the acceleration (i.e. kinetic energy) of the cosmic rays and this changes its kinematics. There are two known proofs of these energy loses: 1) a higher compression factor of the post-shock plasma, 2) a lower post-shock temperature.
The supernova remnant they look at is RCW 86 and for this source the radiation from the ultrarelativistic electrons is what causes the X-ray emission that they analyze. They find that behind this supernova remnant’s northeast shock, the cosmic ray induced pressure is higher than the thermal pressure. This implies that the temperature of the protons in the post-shock is different from the theoretically (i.e. standard) shock heating. This implies that cosmic rays are what produce more than half of the post-shock pressure.
E. A. Helder, J. Vink, C. G. Bassa, A. Bamba, et al. 2009, Science, 325, 719
http://www.sciencemag.org/cgi/content/abstract/325/5941/719
A widely studied topic both by astronomers and physicist today is Cosmic Rays, which are highly energetic particles that originate outside the Earth, travel through the universe, and hit our atmosphere. A known sub-category is that of accelerated cosmic rays and the accelerating process behind it is know to be mostly due to supernova remnants (SNR – expanding plasma shells caused by strong and violent exploding stars into supernovae and its boundary is called a “shock wave”) . This paper discusses one scenario of how a supernova remnant can accelerate the cosmic rays.
It has been found that for the known cosmic ray density to be stable in the Milky Way, every century three supernovae transform a tenth of their kinetic energy in cosmic ray energy. Supernova remnants lose a high amount of energy to the acceleration (i.e. kinetic energy) of the cosmic rays and this changes its kinematics. There are two known proofs of these energy loses: 1) a higher compression factor of the post-shock plasma, 2) a lower post-shock temperature.
The supernova remnant they look at is RCW 86 and for this source the radiation from the ultrarelativistic electrons is what causes the X-ray emission that they analyze. They find that behind this supernova remnant’s northeast shock, the cosmic ray induced pressure is higher than the thermal pressure. This implies that the temperature of the protons in the post-shock is different from the theoretically (i.e. standard) shock heating. This implies that cosmic rays are what produce more than half of the post-shock pressure.
Article Summary #8
EVIDENCE FOR DYNAMICAL CHANGES IN A TRANSITIONAL PROTOPLANETARY DISK WITH MID-INFRARED VARIABILITY
J. Muzerolle et al 2009, ApJ, 704, L15
http://www.iop.org/EJ/abstract/1538-4357/704/1/L15/
Planetary disks are circumstellar, highly dusty disk where planets form around young stars (early stage in the stellar system evolution). Planetary formation is a highly complex phenomenon that so far has been difficult to explain and understand, but the physics structure and evolution of the disk where they form can give more insight into this problem and can constrain the timescales related to planet formation.
So far, it has been known that radiation and viscous energy released from the star heat up the dust in the planetary disk. This hot dust emits radiation in the infrared and can give information about the structure of the disk. This paper presents an investigation conducted in the mid-infrared energy range spectroscopy using data from the Spitzer Space Telescope. The thermal emission from the dust is traced with spectral energy distribution (SED) analysis and with these observations they found the locations of the planet-forming regions in the planetary disk.
Currently, there have been important relationships found between he frequency of the disk and the stellar age and mass, though, in previous investigations what was not taken into consideration, and what this paper focuses on, is the dynamics and accreting behavior of the planetary disk. What they found is a large variability in the height of the disk (seen in the SEDs) and they argue two possible explanations for this behavior: 1) the disk mass-accretion varies in time and that can cause changes in the flux irradiate by the disk and in the in situ density of the disk gas (this theory does not fully explain all the observations yet and needs more supporting evidence); 2) the inner disk becomes dynamically perturbed by either a star or planet and the variations in the emitting are of the inner disk causes shadowing in the outer disk. The presence of that companion (star or planet) can also be explained by a gap in the disk observed in the SED shape.
Further research and long-term infrared monitoring can reveal the periodicity in the flux variations from the disk and the inner disk region could be better resolved with long-baseline interferometry.
J. Muzerolle et al 2009, ApJ, 704, L15
http://www.iop.org/EJ/abstract/1538-4357/704/1/L15/
Planetary disks are circumstellar, highly dusty disk where planets form around young stars (early stage in the stellar system evolution). Planetary formation is a highly complex phenomenon that so far has been difficult to explain and understand, but the physics structure and evolution of the disk where they form can give more insight into this problem and can constrain the timescales related to planet formation.
So far, it has been known that radiation and viscous energy released from the star heat up the dust in the planetary disk. This hot dust emits radiation in the infrared and can give information about the structure of the disk. This paper presents an investigation conducted in the mid-infrared energy range spectroscopy using data from the Spitzer Space Telescope. The thermal emission from the dust is traced with spectral energy distribution (SED) analysis and with these observations they found the locations of the planet-forming regions in the planetary disk.
Currently, there have been important relationships found between he frequency of the disk and the stellar age and mass, though, in previous investigations what was not taken into consideration, and what this paper focuses on, is the dynamics and accreting behavior of the planetary disk. What they found is a large variability in the height of the disk (seen in the SEDs) and they argue two possible explanations for this behavior: 1) the disk mass-accretion varies in time and that can cause changes in the flux irradiate by the disk and in the in situ density of the disk gas (this theory does not fully explain all the observations yet and needs more supporting evidence); 2) the inner disk becomes dynamically perturbed by either a star or planet and the variations in the emitting are of the inner disk causes shadowing in the outer disk. The presence of that companion (star or planet) can also be explained by a gap in the disk observed in the SED shape.
Further research and long-term infrared monitoring can reveal the periodicity in the flux variations from the disk and the inner disk region could be better resolved with long-baseline interferometry.
Article Summary #7
The CoRoT-7 planetary system: two orbiting super-Earths
D. Queloz, F. Bouchy, C. Moutou , 2009, A&A, Volume 506, Number 1
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200913096
Due to the improvement of the searching methods of transient planets, many new exoplanets have been discovered lately and 50 out of hundreds transit their host stars. This type of observation (i.e. being able to observe a planet while it orbits a star) is very useful for detections because constraints can be put on the orbital inclination of the planet and the transit geometry can allow the calculation of the size and mass of the planet. This paper focuses on finding Earth-like planets orbiting the star named CoRoT-7.
The CoRoT Space Telescope is known for having been very useful due to its ability to identify numerous transient sources. The spectrograph on board of this telescope is called HARPS (High Accuracy Radial velocity Planet Searcher) and this is the instrument from which the authors of the paper received their data with which they conducted a radial velocity investigation and they also added ground based photometry data.
By looking at the radial velocity data, they observed a strong variability and a periodic signal which are caused by a transiting planet. Thus, they observed the planet CoRoT-7b, which before that was assumed to be a super-Earth (i.e. planet with similar chemical and atmospheric structure as the Earth, but with a higher mass) and they managed to calculate its mass with a certainty of 20%.
Along with the signal from CoRoT-7b, they noticed a second signal which they investigated in detail and found supporting evidence to attribute it to a second, coplanar Planet, CoRoT-7c. The most intriguing aspect of the results of the authors’ investigation was that both planets appear to be denser than Neptune, so they most probably have a solid/rocky structure like that of the Earth, which is a very important discovery in the search for Earth-like exoplanets.
D. Queloz, F. Bouchy, C. Moutou , 2009, A&A, Volume 506, Number 1
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200913096
Due to the improvement of the searching methods of transient planets, many new exoplanets have been discovered lately and 50 out of hundreds transit their host stars. This type of observation (i.e. being able to observe a planet while it orbits a star) is very useful for detections because constraints can be put on the orbital inclination of the planet and the transit geometry can allow the calculation of the size and mass of the planet. This paper focuses on finding Earth-like planets orbiting the star named CoRoT-7.
The CoRoT Space Telescope is known for having been very useful due to its ability to identify numerous transient sources. The spectrograph on board of this telescope is called HARPS (High Accuracy Radial velocity Planet Searcher) and this is the instrument from which the authors of the paper received their data with which they conducted a radial velocity investigation and they also added ground based photometry data.
By looking at the radial velocity data, they observed a strong variability and a periodic signal which are caused by a transiting planet. Thus, they observed the planet CoRoT-7b, which before that was assumed to be a super-Earth (i.e. planet with similar chemical and atmospheric structure as the Earth, but with a higher mass) and they managed to calculate its mass with a certainty of 20%.
Along with the signal from CoRoT-7b, they noticed a second signal which they investigated in detail and found supporting evidence to attribute it to a second, coplanar Planet, CoRoT-7c. The most intriguing aspect of the results of the authors’ investigation was that both planets appear to be denser than Neptune, so they most probably have a solid/rocky structure like that of the Earth, which is a very important discovery in the search for Earth-like exoplanets.
Article Summary #6
SDSS J013655.91+242546.0 - an A-type hyper-velocity star from the outskirts of the Galaxy
Tillich, A.; Przybilla, N.; Scholz, R.-D.; Heber, U. 2009, Astronomy and Astrophysics, Volume 507, Issue 2, 2009, pp.L37-L40 (A&A Homepage)
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0910.5174
This paper presents an example of a study done on a hyper-velocity star in order to find its point of origin. Hyper-velocity stars are stars that become unbound to the galaxy due to their very high velocities, and sometimes they even escape their host galaxy.
Tilich et al. 2009 explain how the dynamical ejection by a suppermassive black hole can explain how these stars end up having such high velocities. In order to do that, finding the origin of the star and what mechanism explains its ejection is essential.
The first hyper-velocity stars were discovered in 2005 with radial velocity measurements. At this point, there are different opinions that scientists have about the point of origin if these unique stars: some think they form in the Galactic center, while others think that they are born in any area of the galaxy, not necessarily in the center, and their high speeds can be explained as being a cause of the tidal distribution of a dwarf galaxy in the galactic potential.
Since there are no measurements for proper motion, accurate trajectories for this kind of objects have not been found. The closest measurement achieved so far is only that of a high-velocity star (in contrast to a hyper-velocity star), a B-type star for which the trajectory was measured with known proper motions, radial velocity and spectroscopic distance.
That was the first fast star that was found that the star originated in the outer-rim of the galaxy, which proves that such a mechanism is possible. Tilich et al. 2009 managed to find the first hyper-velocity star that did not originate at the center of the galaxy, but also at the rim, and that is an A-type hyper-velocity star and its speed is ~590km/s.
Tillich, A.; Przybilla, N.; Scholz, R.-D.; Heber, U. 2009, Astronomy and Astrophysics, Volume 507, Issue 2, 2009, pp.L37-L40 (A&A Homepage)
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0910.5174
This paper presents an example of a study done on a hyper-velocity star in order to find its point of origin. Hyper-velocity stars are stars that become unbound to the galaxy due to their very high velocities, and sometimes they even escape their host galaxy.
Tilich et al. 2009 explain how the dynamical ejection by a suppermassive black hole can explain how these stars end up having such high velocities. In order to do that, finding the origin of the star and what mechanism explains its ejection is essential.
The first hyper-velocity stars were discovered in 2005 with radial velocity measurements. At this point, there are different opinions that scientists have about the point of origin if these unique stars: some think they form in the Galactic center, while others think that they are born in any area of the galaxy, not necessarily in the center, and their high speeds can be explained as being a cause of the tidal distribution of a dwarf galaxy in the galactic potential.
Since there are no measurements for proper motion, accurate trajectories for this kind of objects have not been found. The closest measurement achieved so far is only that of a high-velocity star (in contrast to a hyper-velocity star), a B-type star for which the trajectory was measured with known proper motions, radial velocity and spectroscopic distance.
That was the first fast star that was found that the star originated in the outer-rim of the galaxy, which proves that such a mechanism is possible. Tilich et al. 2009 managed to find the first hyper-velocity star that did not originate at the center of the galaxy, but also at the rim, and that is an A-type hyper-velocity star and its speed is ~590km/s.
Article Summary #5
The spin-orbit angle of the transiting hot Jupiter CoRoT-1b
Pont, F.; Endl, M.; Cochran, W. D.; Barnes, S. I., et al. , 2010, Volume 402, Issue 1, Pages L1-L5
http://www3.interscience.wiley.com/cgi-bin/fulltext/123208852/HTMLSTART?CRETRY=1&SRETRY=0
This paper presents an extremely interesting result of a measurement of the angle between the orbit of the planet CoRoT-1b and the normal to the rotational axis of its host star.
The Rossier-McKaughlin effect is used to measure the angle between the rotation axis of a star and the orbit plane of one of its orbiting planets. This method involves analyzing the changes in the radial velocity of the star when the planet passes in from of it (this is also called transiting). The observations and analysis of the distribution of these planetary spin-orbit angles are very important for gaining a deeper understanding of the evolution of stellar systems in general.
CoRoT-1b is a hot-Jupiter type of exoplanet, with a very short orbital period of 1.5 days. This quick orbit implies that the massive planet (with approximately the same mass as Jupiter) is very close to its host star from which it absorbs radiation and its temperature increases, thus the name “hot Jupiter”.
For this analysis, the measurements were made with high-accuracy photometry from a camera on the European Southern Observatory in Chile, and with radial velocity spectroscopic data from the spectrographs SOPHIE (Spectrographe pour l’Observation des Phénomènes des Intérieurs stellaires et des Exoplanètes) and HARPS (High Accuracy Radial velocity Planet Searcher). Pont et al. 2010 got the physical parameters of the transit from standard spectroscopic measurements.
The results were unexpected: they found a spin-orbit angle of 77̊, almost perpendicular (in comparison with the inclination of the Earth relative to the sun which is almost zero). They argue that the most probable explanation would be that the hot Jupiter ended up in such an unusual position due to being hit by another object of comparable size.
Pont, F.; Endl, M.; Cochran, W. D.; Barnes, S. I., et al. , 2010, Volume 402, Issue 1, Pages L1-L5
http://www3.interscience.wiley.com/cgi-bin/fulltext/123208852/HTMLSTART?CRETRY=1&SRETRY=0
This paper presents an extremely interesting result of a measurement of the angle between the orbit of the planet CoRoT-1b and the normal to the rotational axis of its host star.
The Rossier-McKaughlin effect is used to measure the angle between the rotation axis of a star and the orbit plane of one of its orbiting planets. This method involves analyzing the changes in the radial velocity of the star when the planet passes in from of it (this is also called transiting). The observations and analysis of the distribution of these planetary spin-orbit angles are very important for gaining a deeper understanding of the evolution of stellar systems in general.
CoRoT-1b is a hot-Jupiter type of exoplanet, with a very short orbital period of 1.5 days. This quick orbit implies that the massive planet (with approximately the same mass as Jupiter) is very close to its host star from which it absorbs radiation and its temperature increases, thus the name “hot Jupiter”.
For this analysis, the measurements were made with high-accuracy photometry from a camera on the European Southern Observatory in Chile, and with radial velocity spectroscopic data from the spectrographs SOPHIE (Spectrographe pour l’Observation des Phénomènes des Intérieurs stellaires et des Exoplanètes) and HARPS (High Accuracy Radial velocity Planet Searcher). Pont et al. 2010 got the physical parameters of the transit from standard spectroscopic measurements.
The results were unexpected: they found a spin-orbit angle of 77̊, almost perpendicular (in comparison with the inclination of the Earth relative to the sun which is almost zero). They argue that the most probable explanation would be that the hot Jupiter ended up in such an unusual position due to being hit by another object of comparable size.
Article Summary #4
Probing the Evolution of Molecular Cloud Structure
J. Kainulainen, H. Beuther, T. Henning, and R. Plume, 2009, A&A 508, L35-L38
http://www.aanda.org.mutex.gmu.edu/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2009/48/aa13605-09/aa13605-09.html
This paper focuses on describing the physical processes inside a molecular cloud, i.e. the way the material is distributed and arranged inside the cloud by calculating the probability distribution of densities in the cloud.
It is known that star formation occurs only in molecular clouds and their structure is very complex and easily affected by the motions created by supersonic turbulences, gas self-gravity and magnetic fields.
For their investigation Kainulainen et al. 2009 chose a sample of molecular clouds complexes within relatively close proximity. The method they used is called the near-infrared dust extinction map technique and with that they derived the extinction of the maps of nearby molecular clouds.
Their results show expected well-fitted log-normal functions at low column densities. Column densities can be derived by measuring the line emission of CO, emission from thermal dust, or from dust extinction. It appears that all clouds with active star formation have a strong excess of high column densities while all quiescent clouds show low excess of high energy clouds.
What they also noticed that the behavior is different at higher column densities where noticeable power law-like wings are present most of the time. These results support the theory that turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but in time gravity becomes predominant.
Thus, the role of the turbulences is important and mostly influences the molecular cloud formation during its early stages, almost to the point where it can be considered the triggering of the active star formation in these molecular clouds.
J. Kainulainen, H. Beuther, T. Henning, and R. Plume, 2009, A&A 508, L35-L38
http://www.aanda.org.mutex.gmu.edu/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2009/48/aa13605-09/aa13605-09.html
This paper focuses on describing the physical processes inside a molecular cloud, i.e. the way the material is distributed and arranged inside the cloud by calculating the probability distribution of densities in the cloud.
It is known that star formation occurs only in molecular clouds and their structure is very complex and easily affected by the motions created by supersonic turbulences, gas self-gravity and magnetic fields.
For their investigation Kainulainen et al. 2009 chose a sample of molecular clouds complexes within relatively close proximity. The method they used is called the near-infrared dust extinction map technique and with that they derived the extinction of the maps of nearby molecular clouds.
Their results show expected well-fitted log-normal functions at low column densities. Column densities can be derived by measuring the line emission of CO, emission from thermal dust, or from dust extinction. It appears that all clouds with active star formation have a strong excess of high column densities while all quiescent clouds show low excess of high energy clouds.
What they also noticed that the behavior is different at higher column densities where noticeable power law-like wings are present most of the time. These results support the theory that turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but in time gravity becomes predominant.
Thus, the role of the turbulences is important and mostly influences the molecular cloud formation during its early stages, almost to the point where it can be considered the triggering of the active star formation in these molecular clouds.
Article Summary #3
A Young Planetary-mass Object in the the ρ Oph Cloud Core
Kenneth A. Marsh et al 2010 ApJ 709 L158-L162
http://www.iop.org/EJ/abstract/2041-8205/709/2/L158/
Stellar clouds are very distant high-density cloud structures where stars are born. A very small object has been found in the ρ Oph cloud core. Cases of planetary-sized objects existing in clusters have been observed before and they are generally only white dwarfs with masses about 13 times that of Jupiter and less.
The big mystery related to the formation of such objects is through what mechanism can there be enough cooling inside a very hot region like a stellar cloud that such a dense and compact object could form (i.e. in order for gravity to overcome the high gas pressure due to the high temperature, strong cooling is needed).
Looking at the near-infrared spectrum, the colors indicate the presence of a low-mass brown dwarf. The region is also very young and it has a high rate of low-mass star formation. Marsh et al. 2010 looked at this cloud also because it is closer than most similar clouds, so the detections are better.
The observational data is in the form of spectroscopic images and it comes from the Two Micron All Sky Survey (2MASS) and from Spitzer IRAC (Infrared Array Camera). The selection was done for brown dwarfs with a relatively low temperature (<2000K) and the objects were found by looking at the K-band continuum images.
The data was fitted with a photospheric model to a grid of synthetic spectra. The spectral morphology is what shows that the brown dwarf is an early T spectral type star, characteristic that is determined from its temperature. It is possible that it might be the youngest star and least massive T-dwarf found so far.
Kenneth A. Marsh et al 2010 ApJ 709 L158-L162
http://www.iop.org/EJ/abstract/2041-8205/709/2/L158/
Stellar clouds are very distant high-density cloud structures where stars are born. A very small object has been found in the ρ Oph cloud core. Cases of planetary-sized objects existing in clusters have been observed before and they are generally only white dwarfs with masses about 13 times that of Jupiter and less.
The big mystery related to the formation of such objects is through what mechanism can there be enough cooling inside a very hot region like a stellar cloud that such a dense and compact object could form (i.e. in order for gravity to overcome the high gas pressure due to the high temperature, strong cooling is needed).
Looking at the near-infrared spectrum, the colors indicate the presence of a low-mass brown dwarf. The region is also very young and it has a high rate of low-mass star formation. Marsh et al. 2010 looked at this cloud also because it is closer than most similar clouds, so the detections are better.
The observational data is in the form of spectroscopic images and it comes from the Two Micron All Sky Survey (2MASS) and from Spitzer IRAC (Infrared Array Camera). The selection was done for brown dwarfs with a relatively low temperature (<2000K) and the objects were found by looking at the K-band continuum images.
The data was fitted with a photospheric model to a grid of synthetic spectra. The spectral morphology is what shows that the brown dwarf is an early T spectral type star, characteristic that is determined from its temperature. It is possible that it might be the youngest star and least massive T-dwarf found so far.
Article Summary #2
New Method of Determining the Milky Way Bar Patten Speed
I. Minchev, J. Nordhaus, A. C. Quillen, 2010, eprint arXiv:1002.1742, (Mem. S.A.It. Vol. 00, 189)
http://arxiv.org/abs/1002.1742v1
Modeling of the galaxies and the Milky Way specifically, has been an interest for astronomers for many years. Even though in the past the galaxies have been modeled as a perfectly symmetric disk, due to the increase of the amount and quality of data that astronomers can use nowadays, the realistic asymmetries seen in galaxies have become more and more important for constructing accurate galactic models.
The galaxy that would seem the easiest to observe and model is the Milky Way, but difficulties and problems occur in the observations due to the fact that we are located inside the galaxy and an outside observation is currently not possible.
Galaxy modeling is done through numerical simulations, and Minchev et al. 2010 have managed to perform a two-dimensional simulation with a test-particle. The simulation was done initially for a symmetric disk through numerical integration. They simulated measurements of the Oort Constant (C) value in a gravitational potential adding the Galactic bar to their calculations. This value determines the relationship between the gradients of the velocities in the galaxy. The important aspect that resulted from these simulations is that the Oort C value becomes more negative as the velocity dispersion increases.
These results are very useful because they can help improve the previous models. This can be done simply by measuring the Oort Constant values in our galaxy with observational data and then comparing them with the values resulted from the simulations. Also, what influences the value of the Oort Constant is the pattern speed of the galactic bar in the center of the Milky Way.
I. Minchev, J. Nordhaus, A. C. Quillen, 2010, eprint arXiv:1002.1742, (Mem. S.A.It. Vol. 00, 189)
http://arxiv.org/abs/1002.1742v1
Modeling of the galaxies and the Milky Way specifically, has been an interest for astronomers for many years. Even though in the past the galaxies have been modeled as a perfectly symmetric disk, due to the increase of the amount and quality of data that astronomers can use nowadays, the realistic asymmetries seen in galaxies have become more and more important for constructing accurate galactic models.
The galaxy that would seem the easiest to observe and model is the Milky Way, but difficulties and problems occur in the observations due to the fact that we are located inside the galaxy and an outside observation is currently not possible.
Galaxy modeling is done through numerical simulations, and Minchev et al. 2010 have managed to perform a two-dimensional simulation with a test-particle. The simulation was done initially for a symmetric disk through numerical integration. They simulated measurements of the Oort Constant (C) value in a gravitational potential adding the Galactic bar to their calculations. This value determines the relationship between the gradients of the velocities in the galaxy. The important aspect that resulted from these simulations is that the Oort C value becomes more negative as the velocity dispersion increases.
These results are very useful because they can help improve the previous models. This can be done simply by measuring the Oort Constant values in our galaxy with observational data and then comparing them with the values resulted from the simulations. Also, what influences the value of the Oort Constant is the pattern speed of the galactic bar in the center of the Milky Way.
Article Summary #1
Pattern Speeds in Interacting Galaxies
Dobbs, C. L., 2010, eprint arXiv:1002.1269, (Mem. S.A.It. Vol. 00, 107)
http://arxiv.org/abs/1002.1269v1
Spiral patterns are the arrangements that are known to exist in spiral galaxies and that can also form as a result of galaxies interacting with each other. They are known to be driven by bars, i.e. the central structure of some galaxies.
With the use of numerical simulations, Dobbs 2010 perform an investigation on the interaction between galaxies. The software that they used for the creation of the simulations is SPH (Smoothed Particle Hydrodynamics code) and they created a model for a galaxy interacting system.
The modeling of the interior of the galaxies was done under different initial conditions, and, even though the spiral arms exhibit different pattern speeds, these speeds decrease as with an increase in the radius.
The overall calculations were performed with different types of galaxies (related to their structure): stellar, gaseous, mixed stellar and gaseous, and the interaction with an orbiting galaxy. Across the disk of the resulting galaxy, the pattern speed is not constant in time, and they are also different for each arm. They find a maximum pattern speed of ~20km/s/kpc for the disks that have a live stellar component. The speed decreases by a factor of four at the end of the spiral arm. When only the gas is modeled, the speeds are in most cases very small (5 km/s/kpc) at all radii. Finally, when they do the simulation with mixed stellar and gaseous galaxies they noticed that the gas tends to follow the stellar distribution, thus increasing the pattern speeds.
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