Probing planetary atmospheres is tricky business at the best of times, but when you’re limited to planets you can’t even see, the project seems well nigh insurmountable. Nonetheless, astronomers using the Spitzer space telescope are having some success working in the infrared. They focus on transiting hot Jupiters, and earlier this year were able to obtain spectra of exoplanetary light from two such worlds, HD 189733b and HD 209458b.
We discussed that work earlier and noted that no water vapor was found in the atmosphere of either planet, despite earlier predictions that it would be. Now a team led by Giovanna Tinetti (Institute d’Astrophysique de Paris) has made further observations of HD 189733b, studying changes in the infrared light from the star as the planet transits, and thus filters the light through its own planetary atmosphere. Working at three different wavelengths, the study showed the clear signature of water.
Image: This plot of data from NASA’s Spitzer Space Telescope tells astronomers that a toasty gas exoplanet, or a planet beyond our solar system, contains water vapor. Spitzer observed the planet, called HD 189733b, cross in front of its star at three different infrared wavelengths: 3.6 microns, 5.8 microns, and 8 microns (see lime-colored dots). For each wavelength, the planet’s atmosphere absorbed different amounts of the starlight that passed through it. The pattern by which this absorption varies with wavelength matches known signatures of water, as shown by the theoretical model in blue. Credit: ESA, NASA/ JPL-Caltech/G. Tinetti (Institute d’Astrophysique de Paris, University College London).
“Water is the only molecule that can explain that behavior,” said Tinetti. “Observing primary eclipses in infrared light is the best way to search for this molecule in exoplanets.”
By ‘primary eclipse,’ Tinetti refers to the planet crossing directly in front of the star. The earlier Spitzer work on HD 189733b and HD 209458b was performed during ‘secondary’ eclipses when the planets moved back behind their stars after the transit. Tinetti clearly believes the primary eclipse is the way to go, a thought backed by visible-light studies of HD 209458b, in which astronomers using the Hubble Space Telescope found hints of water there by studying the planet during a primary eclipse.
But clearly, that water is not liquid. The average temperature on HD 189733b is, at best estimate, 1000 Kelvin (1340 degrees Fahrenheit, or 727 degrees Celsius). We’re talking about a planet that orbits its star in a mere two days. Even so, this hot Jupiter, some 63 light years away in the constellation Vulpecula, may be telling us that water is as abundant in at least one other solar system as it is in our own. And that finding may one day extend to smaller rocky worlds around stars like this one.
The paper is Tinetti et al., “Water vapour in the atmosphere of a transiting extrasolar planet,” Nature 448, (12 July 2007), pp. 169-171, with abstract available.
Benchmark Survey Shows that Giant Outer Extrasolar Planets are Rare
http://www.spaceref.com/news/viewpr.nl.html?pid=23043
“Astronomers who used powerful telescopes in Arizona and Chile in a survey
for planets around nearby stars have discovered that extrasolar planets
more massive than Jupiter are extremely rare in other outer solar systems.”
Now what would be really interesting would be to do a similar analysis for Gliese 436 b: the question of whether the planet is truly a hot ice planet, or a terrestrial planet with a massive atmosphere is still open, though the former is considered more likely.
Water vapour in the atmosphere of a transiting extrasolar planet
Authors: Giovanna Tinetti, Alfred Vidal-Madjar, Mao-Chang Liang, Jean-Philippe Beaulieu, Yuk Yung, Sean Carey, Robert J. Barber, Jonathan Tennyson, Ignasi Ribas, Nicole Allard, Gilda E. Ballester, David K. Sing, Franck Selsis
(Submitted on 20 Jul 2007)
Abstract: Water is predicted to be among, if not the most abundant molecular species after hydrogen in the atmospheres of close-in extrasolar giant planets (hot-Jupiters) Several attempts have been made to detect water on an exoplanet, but have failed to find compelling evidence for it or led to claims that should be taken with caution. Here we report an analysis of recent observations of the hot-Jupiter HD189733b taken during the transit, where the planet passed in front of its parent star. We find that absorption by water vapour is the most likely cause of the wavelength-dependent variations in the effective radius of the planet at the infrared wavelengths 3.6, 5.8 and 8 microns. The larger effective radius observed at visible wavelengths may be due to either star variability or the presence of clouds/hazes. We explain the most recent thermal infrared observations of the planet during secondary transit behind the star, reporting a non-detection of water on HD189733b, as being a consequence of the nearly isothermal vertical profile of the planet’s atmosphere. Our results show that water is detectable on extrasolar planets using the primary transit technique and that the infrared should be a better wavelength region than the visible, for such searches.
Subjects: Astrophysics (astro-ph)
Journal reference: Nature 2007, 448, p 163
Cite as: arXiv:0707.3064v1 [astro-ph]
Submission history
From: Beaulieu [view email]
[v1] Fri, 20 Jul 2007 15:57:14 GMT (297kb)
http://arxiv.org/abs/0707.3064
A Spitzer Search for Water in the Transiting Exoplanet HD189733b
Authors: David Ehrenreich (IAP), Guillaume Hébrard (IAP), Alain Lecavelier Des Etangs (IAP), David K Sing (IAP), Jean-Michel Désert (IAP), François Bouchy (IAP), Roger Ferlet (IAP), Alfred Vidal-Madjar (IAP)
(Submitted on 5 Sep 2007)
Abstract: We present Spitzer Space Telescope observations of the extrasolar planet HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with the Infrared Array Camera. The system parameters, including planetary radius, stellar radius, and impact parameter are derived from fits to the transit light curves at both wavelengths. We measure two consistent planet-to-star radius ratios, (Rp/Rs)[3.6$\mu$m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and (Rp/Rs)[5.8$\mu$m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include both the random and systematic errors in the transit baseline. Although planet radii are determined at 1%-accuracy, if all uncertainties are taken into account the resulting error bars are still too large to allow for the detection of atmospheric constituants like water vapour. This illustrates the need to observe multiple transits with the longest possible out-of-transit baseline, in order to achieve the precision required by transmission spectroscopy of giant extrasolar planets.
Comments: Accepted in The Astrophysical Journal Letters
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0709.0576v1 [astro-ph]
Submission history
From: David Ehrenreich [view email] [via CCSD proxy]
[v1] Wed, 5 Sep 2007 06:52:46 GMT (279kb)
http://arxiv.org/abs/0709.0576
Theoretical Spectral Models of the Planet HD 209458b with a Thermal Inversion and Water Emission Bands
Authors: Adam Burrows, Ivan Hubeny, Jano Budaj, Heather Knutson, David Charbonneau
(Submitted on 25 Sep 2007)
Abstract: We find that a theoretical fit to all the HD 209458b data at secondary eclipse requires that the dayside atmosphere of HD 209458b have a thermal inversion and a stratosphere. This inversion is caused by the capture of optical stellar flux by an absorber of uncertain origin that resides at altitude. One consequence of stratospheric heating and temperature inversion is the flipping of water absorption features into emission features from the near- to the mid-infrared and we see evidence of such a water emission feature in the recent HD 209458b IRAC data of Knutson et al. In addition, an upper-atmosphere optical absorber may help explain both the weaker-than-expected Na D feature seen in transit and the fact that the transit radius at 24 $\mu$m is smaller than the corresponding radius in the optical. Moreover, it may be a factor in why HD 209458b’s optical transit radius is as large as it is. We speculate on the nature of this absorber and the planets whose atmospheres may, or may not, be affected by its presence.
Comments: Accepted to the Astrophysical Journal Letters on August 28, 2007, six pages in emulateapj format
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0709.3980v1 [astro-ph]
Submission history
From: Adam Burrows [view email]
[v1] Tue, 25 Sep 2007 16:06:07 GMT (54kb)
http://arxiv.org/abs/0709.3980
The 3.6-8.0 Micron Broadband Emission Spectrum of HD 209458b: Evidence for an Atmospheric Temperature Inversion
Authors: Heather A. Knutson, David Charbonneau, Lori E. Allen, Adam Burrows, S. Thomas Megeath
(Submitted on 25 Sep 2007)
Abstract: We estimate the strength of the bandpass-integrated thermal emission from the extrasolar planet HD 209458b at 3.6, 4.5, 5.8, and 8.0 microns using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We observe a single secondary eclipse simultaneously in all four bandpasses and find relative eclipse depths of 0.00094 +/- 0.00009, 0.00213 +/- 0.00015, 0.00301 +/- 0.00043, and 0.00240 +/- 0.00026, respectively. These eclipse depths reveal that the shape of the inferred emission spectrum for the planet differs significantly from the predictions of standard atmosphere models; instead the most plausible explanation would require the presence of an inversion layer high in the atmosphere leading to significant water emission in the 4.5 and 5.8 micron bandpasses. This is the first clear indication of such a temperature inversion in the atmosphere of a hot Jupiter, as previous observations of other planets appeared to be in reasonably good agreement with the predictions of models without such an inversion layer.
Comments: 14 pages, 3 figures, accepted for publication in ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0709.3984v1 [astro-ph]
Submission history
From: Heather Knutson [view email]
[v1] Tue, 25 Sep 2007 16:15:58 GMT (35kb)
http://arxiv.org/abs/0709.3984
Inflated planets and their low-mass companions
Authors: Rosemary A. Mardling
(Submitted on 1 Oct 2007)
Abstract: Various mechanisms have been proposed to explain the inflated size of HD 209458b after it became clear that it has no companions capable of producing a stellar reflex velocity greater than around 5 m/s. Had there been such a companion, the hypothesis that it forces the eccentricity of the inflated planet thereby tidally heating it may have been readily accepted.
Here we summarize a paper by the author which shows that companion planets with masses as low as a fraction of an Earth mass are capable of sustaining a non-zero eccentricity in the observed planet for at least the age of the system. While such companions produce stellar reflex velocities which are fractions of a meter per second and hence are below the stellar jitter limit, they are consistent with recent theoretical work which suggests that the planet migration process often produces low-mass companions to short-period giants.
Comments: 4 pages, 3 figures, to appear in “Extreme Solar Systems”, D. Fischer, F. Rasio, S. Thorsett and A. Wolszczan (eds), ASP Conf. Ser., 2007
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0710.0378v1 [astro-ph]
Submission history
From: Rosemary Mardling [view email]
[v1] Mon, 1 Oct 2007 20:14:58 GMT (70kb)
http://arxiv.org/abs/0710.0378
arXiv:0710.3461
Date: Thu, 18 Oct 2007 09:00:31 GMT (1255kb)
Title: The Frequency of Large Radius Hot and Very Hot Jupiters in omega
Centauri
Authors: David T F Weldrake (1), Penny D Sackett (2) and Terry J Bridges (3).
((1) MPIA, Heidelberg, (2) RSAA, Mount Stromlo Observatory, (3) Queen’s
University)
Categories: astro-ph
Comments: 22 pages, 8 figures, accepted for publication in ApJ
We present the results of a deep, wide-field search for transiting `Hot
Jupiter (HJ)’ planets in the globular cluster omega Centauri. As a result of a
25-night observing run with the ANU 40-inch telescope at Siding Spring
Observatory, a total of 109,726 stellar time series composed of 787 independent
data points were produced with differential photometry in a 52×52′ (0.75 deg^2)
field centered on the cluster core, but extending well beyond. Taking into
account the size of transit signals as a function of stellar radius, 45,406
stars have suitable photometric accuracy (less than =0.045 mag to V=19.5) to search for
transits. Of this sample, 31,000 stars are expected to be main sequence cluster
members. All stars, both cluster and foreground, were subjected to a rigorous
search for transit signatures; none were found. Extensive Monte Carlo
simulations based on our actual data set allows us to determine the sensitivity
of our survey to planets with radii ~1.5R_Jup, and thus place statistical upper
limits on their occurrence frequency ‘F’. Smaller planets are undetectable in
our data. At 95% confidence, the frequency of Very Hot Jupiters (VHJs) with
periods P satisfying 1d less than P less than 3d can be no more than F_VHJ less than 1/1040 in omega Cen.
For HJ and VHJ distributed uniformly over the orbital period range 1d less than P less than 5d,
F_VHJ+HJ less than 1/600. Our limits on large, short-period planets are comparable to
those recently reported for other Galactic fields, despite being derived with
less telescope time.
http://arxiv.org/abs/0710.3461 , 1255kb
Exoplanet HD209458b: inflated hydrogen atmosphere but no sign of evaporation
Authors: Lotfi Ben-Jaffel
(Submitted on 9 Nov 2007)
Abstract: Many extrasolar planets orbit closely to their parent star. Their existence raises the fundamental problem of loss and gain in their mass. For exoplanet HD209458b, reports on an unusually extended hydrogen corona and a hot layer in the lower atmosphere seem to support the scenario of atmospheric inflation by the strong stellar irradiation. However, difficulties in reconciling evaporation models with observations call for a reassessment of the problem. Here, we use HST archive data to report a new absorption rate of $\sim 8.9%\pm 2.1$% by atomic hydrogen during the HD209458b transit, and show that no sign of evaporation could be detected for the exoplanet. We also report evidence of time variability in the HD209458 Ly-a flux, a variability that was not accounted for in previous studies, which corrupted their diagnostics. Mass loss rates thus far proposed in the literature in the range $5\times 10^{10}-10^{11} {\rm g s^{-1}}$ must induce a spectral signature in the Lyman-$\alpha$ line profile of HD209458 that cannot be found in the present analysis. Either an unknown compensation effect is hiding the expected spectral feature or else the mass loss rate of neutrals from HD209458 is modest.
Comments: 5 pages, 3 figures, 1 table
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0711.1432v1 [astro-ph]
Submission history
From: Lotfi Ben-Jaffel [view email]
[v1] Fri, 9 Nov 2007 10:33:38 GMT (257kb)
http://arxiv.org/abs/0711.1432
Primary transit of the planet HD189733b at 3.6 and 5.8 microns
Authors: J.P. Beaulieu, S. Carey, I. Ribas, G. Tinetti
(Submitted on 14 Nov 2007)
Abstract: The hot Jupiter HD 189733b was observed during its primary transit using the Infrared Array Camera on the Spitzer Space Telescope. The transit depths were measured simultaneously at 3.6 and 5.8 microns. Our analysis yields values of 2.356 +- 0.019 % and 2.436 +- 0.020$ % at 3.6 and 5.8 microns respectively, for a uniform source. We estimated the contribution of the limb-darkening and star-spot effects on the final results. We concluded that although the limb darkening increases by ~0.02-0.03 % the transit depths, and the differential effects between the two IRAC bands is even smaller, 0.01 %. Furthermore, the host star is known to be an active spotted K star with observed photometric modulation. If we adopt an extreme model of 20 % coverage with spots 1000K cooler of the star surface, it will make the observed transits shallower by 0.19 and 0.18 %. The difference between the two bands will be only of 0.01 %, in the opposite direction to the limb darkening correction. If the transit depth is affected by limb darkening and spots, the differential effects between the 3.6 and 5.8 microns bands are very small. The differential transit depths at 3.6 and 5.8 microns and the recent one published by Knutson et al.(2007) at 8 microns are in agreement with the presence of water vapour in the upper atmosphere of the planet. This is the companion paper to Tinetti et al. (2007b), where the detailed atmosphere models are presented.
Comments: 6 pages, 4 figures, Astrophysical Journal
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0711.2142v1 [astro-ph]
Submission history
From: Jean-Philippe Beaulieu [view email]
[v1] Wed, 14 Nov 2007 10:02:48 GMT (290kb)
http://arxiv.org/abs/0711.2142
A Technique for Detecting Starlight Scattered from Transiting Extrasolar Planets with Application to HD 209458b
Authors: Xin Liu, Edwin L. Turner, Norio Narita, Yasushi Suto, Joshua N. Winn, Toru Yamada, Bun’ei Sato, Wako Aoki, Motohide Tamura
(Submitted on 14 Nov 2007)
Abstract: We present a new technique for detecting scattered starlight from transiting, close-orbiting extrasolar giant planets (CEGPs) that has the virtues of simplicity, robustness, linearity, and model-independence. Given a series of stellar spectra obtained over various phases of the planetary orbit, the goal is to measure the strength of the component scattered by the planet relative to the component coming directly from the star. We use two complementary strategies, both of which rely on the predictable Doppler shifts of both components and on combining the results from many spectral lines and many exposures. In the first strategy, we identify segments of the stellar spectrum that are free of direct absorption lines and add them after Doppler-shifting into the planetary frame. In the second strategy, we compare the distribution of equivalent-width ratios of the scattered and direct components. Both strategies are calibrated with a “null test” in which scrambled Doppler shifts are applied to the spectral segments.
As an illustrative test case, we apply our technique to spectra of HD 209458 taken when the planet was near opposition (with orbital phases ranging from 11 to 34$\arcdeg$, where 0$\arcdeg$ is at opposition), finding that the planet-to-star flux ratio is $(1.4 \pm 2.9)\times10^{-4}$ in the wavelength range 554$-$681 nm. This corresponds to a geometric albedo of $0.8 \pm 1.6$, assuming the phase function of a Lambert sphere. Although the result is not statistically significant, the achieved sensitivity and relatively small volume of data upon which it is based are very encouraging for future ground-based spectroscopic studies of scattered light from transiting CEGP systems.
Comments: 8 pages, 4 figures; Submitted to ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0711.2304v1 [astro-ph]
Submission history
From: Xin Liu [view email]
[v1] Wed, 14 Nov 2007 21:02:51 GMT (58kb)
http://arxiv.org/abs/0711.2304
The Very Low Albedo of an Extrasolar Planet: MOST Spacebased Photometry of HD 209458
Authors: Jason F. Rowe, Jaymie M. Matthews, Sara Seager, Eliza Miller-Ricci, Dimitar Sasselov, Rainer Kuschnig, David B. Guenther, Anthony F. J. Moffat, Slavek M. Rucinski, Gordon A. H. Walker, Werner W. Weiss
(Submitted on 26 Nov 2007)
Abstract: Measuring the albedo of an extrasolar planet provides insights into its atmospheric composition and its global thermal properties, including heat dissipation and weather patterns. Such a measurement requires very precise photometry of a transiting system sampling fully many phases of the secondary eclipse.
Spacebased optical photometry of the transiting system HD 209458 from the MOST (Microvariablity and Oscillations of STars) satellite, spanning 14 and 44 days in 2004 and 2005 respectively, allows us to set a sensitive limit on the optical eclipse of the hot exosolar giant planet in this system.
Our best fit to the observations yields a flux ratio of the planet and star of 7 $\pm$ 9 ppm (parts per million), which corresponds to a geometric albedo through the MOST bandpass (400-700 nm) of $A_g$ = 0.038 $\pm$ 0.045. This gives a 1$\sigma$ upper limit of 0.08 for the geometric albedo and a 3$\sigma$ upper limit of 0.17. HD 209458b is significantly less reflective than Jupiter (for which $A_g$ would be about 0.5).
This low geometric albedo rules out the presence of bright reflective clouds in this exoplanet’s atmosphere. We determine refined parameters for the star and exoplanet in the HD 209458 system based on a model fit to the MOST light curve.
Comments: 22 pages, 8 figures, submitted to the ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0711.4111v1 [astro-ph]
Submission history
From: Jason F. Rowe [view email]
[v1] Mon, 26 Nov 2007 21:00:15 GMT (137kb)
http://arxiv.org/abs/0711.4111
First detection of polarized scattered light from an exoplanetary atmosphere
Authors: S.V. Berdyugina, A.V. Berdyugin, D.M. Fluri, V. Piirola
(Submitted on 2 Dec 2007)
Abstract: We report the first direct detection of an exoplanet in polarized scattered light. The transiting planet HD189733b is one of the very hot Jupiters with shortest periods and, thus, smallest orbits, which makes them ideal candidates for polarimetric detections. We obtained polarimetric measurements of HD189733 in the $B$ band well distributed over the orbital period and detected two polarization maxima near planetary elongations with the peak amplitude of $\sim2\cdot10^{-4}$. Assuming Rayleigh scattering, we estimated the effective size of the scattering atmosphere (Lambert sphere) to be 1.5$\pm$0.2 $R_{\rm J}$, which is 30% larger than the radius of the opaque body previously inferred from transits. If the scattering matter fills the planetary Roche lobe, the lower limit of the geometrical albedo can be estimated as 0.14. The phase dependence of polarization indicates that the planetary orbit is oriented almost in the north-south direction with the longitude of the ascending node $\Omega$=(16\degr or 196\degr)$\pm$8\degr. We obtain independent estimates of the orbit inclination $i$=98\degr$\pm$8\degr and eccentricity $e$=0.0 (with the uncertainty of 0.05) which are in excellent agreement with values determined previously from transits and radial velocities. Our findings clearly demonstrate the power of polarimetry and open a new dimension in exploring exoplanetary atmospheres even for systems without transits.
Comments: accepted in ApJL
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0712.0193v1 [astro-ph]
Submission history
From: Svetlana Berdyugina [view email]
[v1] Sun, 2 Dec 2007 22:39:07 GMT (86kb)
http://arxiv.org/abs/0712.0193
Exoplanet HD 209458b : Evaporation strengthened
Authors: A. Vidal-Madjar, A. Lecavelier des Etangs, J.-M. Desert, G. E. Ballester, R. Ferlet, G. Hebrard, M. Mayor
(Submitted on 5 Feb 2008)
Abstract: Following re-analysis of Hubble Space Telescope observations of primary transits of the extrasolar planet HD209458b at Lyman-alpha, Ben-Jaffel (2007, BJ007) claims that no sign of evaporation is observed. Here we show that, in fact, this new analysis is consistent with the one of Vidal-Madjar et al. (2003, VM003) and supports the detection of evaporation. The apparent disagreement is mainly due to the disparate wavelength ranges that are used to derive the transit absorption depth. VM003 derives a (15+/-4)% absorption depth during transit over the core of the stellar Lyman-alpha line (from -130 km/s to +100 km/s), and this result agrees with the (8.9+/-2.1)% absorption depth reported by BJ007 from a slightly expanded dataset but over a larger wavelength range (+/-200 km/s). These measurements agree also with the (5+/-2)% absorption reported by Vidal-Madjar et al. (2004) over the whole Lyman-alpha line from independent, lower-resolution data. We show that stellar Lyman-alpha variability is unlikely to significantly affect those detections. The HI atoms must necessarily have velocities above the escape velocities and/or be outside the Roche lobe, given the lobe shape and orientation. Absorption by HI in HD209458b’s atmosphere has thus been detected with different datasets, and now with independent analyses. All these results strengthen the concept of evaporating hot-Jupiters, as well as the modelization of this phenomenon.
Comments: To be published in ApJL
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.0587v1 [astro-ph]
Submission history
From: Alain Lecavelier des Etangs [view email]
[v1] Tue, 5 Feb 2008 11:15:11 GMT (144kb)
http://arxiv.org/abs/0802.0587
MOST Spacebased Photometry of the Transiting Exoplanet System HD 209458: Transit Timing to Search for Additional Planets
Authors: E. Miller-Ricci, J.F. Rowe, D. Sasselov, J.M. Matthews, D.B. Guenther, R. Kuschnig, A.F.J Moffat, S.M. Rucinski, G.A.H Walker, W.W. Weiss
(Submitted on 5 Feb 2008)
Abstract: We report on the measurement of transit times for the HD 209458 planetary system from photometry obtained with the MOST (Microvariability & Oscillations of STars) space telescope. Deviations from a constant orbital period can indicate the presence of additional planets in the system that are yet undetected, potentially with masses approaching an Earth mass.
The MOST data sets of HD 209458 from 2004 and 2005 represent unprecedented time coverage with nearly continuous observations spanning 14 and 43 days and monitoring 3 transits and 12 consecutive transits, respectively.
The transit times we obtain show no variations on three scales: (a) no long-term change in P since before 2004 at the 25 ms level, (b) no trend in transit timings during the 2005 run, and (c) no individual transit timing deviations above 80 sec level. Together with previously published transit times from Agol & Steffen (2007), this allows us to place limits on the presence of additional close-in planets in the system, in some cases down to below an Earth mass.
This result, along with previous radial velocity work, now eliminates the possibility that a perturbing planet could be responsible for the additional heat source needed to explain HD 209458b’s anomalous low density.
Comments: 21 pages, 6 figures, accepted to the ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.0718v1 [astro-ph]
Submission history
From: Eliza Miller-Ricci [view email]
[v1] Tue, 5 Feb 2008 22:22:30 GMT (212kb)
http://arxiv.org/abs/0802.0718
Energetic neutral atoms as the explanation for the high velocity hydrogen around HD 209458b
Authors: M. Holmström, A. Ekenbäck, F. Selsis, T. Penz, H. Lammer, P. Wurz
(Submitted on 20 Feb 2008)
Abstract: Absorption in the stellar Lyman-$\alpha$ (Ly-$\alpha$) line observed during the transit of the extrasolar planet HD 209458b reveals high velocity atomic hydrogen at great distances from the planet. This has been interpreted as hydrogen atoms escaping from the exosphere of the planet, possibly undergoing hydrodynamic blow-off, being accelerated by stellar radiation pressure. However, around solar system planets the production of energetic neutral atoms from charge exchange between solar wind protons and neutral hydrogen from the exospheres has been observed, and should also occur at extrasolar planets.
Here we show that the measured transit-associated Ly-$\alpha$ absorption can be explained by the interaction between the exosphere of HD 209458b and the stellar wind, and that radiation pressure alone cannot explain the observation.
This is the first observation of energetic neutral atoms outside the solar system. Since the stellar wind protons are the source of the observed energetic neutral atoms, this provides a completely new method of probing stellar wind conditions, and our model suggests a slow and hot stellar wind near HD 209458b at the time of the observation.
Comments: 11 pages, 3 figures
Subjects: Astrophysics (astro-ph)
Journal reference: Nature, 451, 970-972, 2008.
DOI: 10.1038/nature06600
Cite as: arXiv:0802.2764v1 [astro-ph]
Submission history
From: Mats Holmstr\”om [view email]
[v1] Wed, 20 Feb 2008 11:22:01 GMT (185kb,D)
http://arxiv.org/abs/0802.2764
HST/STIS Optical Transit Transmission Spectra of the hot-Jupiter HD209458b
Authors: David K. Sing, A. Vidal-Madjar, J.-M. Desert, A. Lecavelier des Etangs, G. Ballester
(Submitted on 26 Feb 2008)
Abstract: We present the transmission spectra of the hot-Jupiter HD209458b taken with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Our analysis combines data at two resolutions and applies a complete pixel-by-pixel limb-darkening correction to fully reveal the spectral line shapes of atmospheric absorption features. Terrestrial-based Na I and H I contamination are identified which mask the strong exoplanetary absorption signature in the Na core, which we find reaches total absorption levels of ~0.11% in a 4.4 Ang band. The Na spectral line profile is characterized by a wide absorption profile at the lowest absorption depths, and a sharp transition to a narrow absorption profile at higher absorption values. The transmission spectra also shows the presence of an additional absorber at ~6,250 Ang, observed at both medium and low resolutions.
We performed various limb-darkening tests, including using high precision limb-darkening measurements of the sun to characterize a general trend of Atlas models to slightly overestimate the amount of limb-darkening at all wavelengths, likely due to the limitations of the model’s one-dimensional nature. We conclude that, despite these limitations, Atlas models can still successfully model limb-darkening in high signal-to-noise transits of solar-type stars, like HD209458, to a high level of precision over the entire optical regime (3,000-10,000 Ang) at transit phases between 2nd and 3rd contact.
Comments: 9 pages, 11 figures, submitted to ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.3864v1 [astro-ph]
Submission history
From: David Sing [view email]
[v1] Tue, 26 Feb 2008 18:17:59 GMT (139kb)
http://arxiv.org/abs/0802.3864
Tidal Heating of Extra-Solar Planets
Authors: Brian Jackson, Richard Greenberg, Rory Barnes
(Submitted on 29 Feb 2008)
Abstract: Extra-solar planets close to their host stars have likely undergone significant tidal evolution since the time of their formation. Tides probably dominated their orbital evolution once the dust and gas had cleared away, and as the orbits evolved there was substantial tidal heating within the planets. The tidal heating history of each planet may have contributed significantly to the thermal budget that governed the planet’s physical properties, including its radius, which in many cases may be measured by observing transit events. Typically, tidal heating increases as a planet moves inward toward its star and then decreases as its orbit circularizes.
Here we compute the plausible heating histories for several planets with measured radii, using the same tidal parameters for the star and planet that had been shown to reconcile the eccentricity distribution of close-in planets with other extra-solar planets. Several planets are discussed, including for example HD 209458 b, which may have undergone substantial tidal heating during the past billion years, perhaps enough to explain its large measured radius. Our models also show that GJ 876 d may have experienced tremendous heating and is probably not a solid, rocky planet. Theoretical models should include the role of tidal heating, which is large, but time-varying.
Comments: Accepted for publication to ApJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0803.0026v1 [astro-ph]
Submission history
From: Brian Jackson [view email]
[v1] Fri, 29 Feb 2008 23:04:38 GMT (803kb)
http://arxiv.org/abs/0803.0026
Determining atmospheric conditions at the terminator of the hot-Jupiter HD209458b
Authors: David K. Sing, A. Vidal-Madjar, A. Lecavelier des Etangs, J.-M. Desert, G. Ballester, D. Ehrenreich
(Submitted on 7 Mar 2008)
Abstract: We present a theoretical model fit to the HST/STIS optical transit transmission spectra of HD209458b. In our fit, we use the sodium absorption line profile along with the Rayleigh scattering by H2 to determine the average temperature-pressure profile at the planetary terminator, and infer the abundances of atomic and molecular species. The observed sodium line profile spans an altitude range of ~3,500 km, corresponding to pressures between ~0.001 and 50 mbar in our atmospheric model.
We find that the sodium line profile requires condensation at pressures lower than ~3 mbar, presumably into sodium sulfide, depleting atomic sodium only at high altitudes. The condensation of sodium is supported by an observed sudden abundance change, from 2 times solar abundance in the lower atmosphere to 0.2 in the upper atmosphere, within a low temperature region which falls below that of the chemical equilibrium condensation curve of sodium sulfide.
Our findings also indicate the presence of a hot atmosphere near stratospheric altitudes corresponding to pressures of ~30 mbar, consistent with that of the observed dayside temperature inversion. In addition, we find a separate higher altitude temperature rise, corresponding to pressures around ~0.01 mbar. This higher altitude temperature rise indicates that absorption by atomic sodium can potentially probe the bottom of the thermosphere, and might possibly be sensitive to the temperature rise linked with atmospheric escape.
Comments: 7 pages, 3 figures, submitted to Astrophysical Journal
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0803.1054v1 [astro-ph]
Submission history
From: David Sing [view email]
[v1] Fri, 7 Mar 2008 10:55:22 GMT (39kb)
http://arxiv.org/abs/0803.1054
Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
Authors: A. Burrows, L. Ibgui, I. Hubeny
(Submitted on 17 Mar 2008)
Abstract: We calculate a new suite of albedo models for close-in extrasolar giant planets and compare with the recent stringent upper limit for HD 209458b of Rowe et al. using MOST. We find that all models without scattering clouds are consistent with this optical limit.
We explore the dependence on wavelength and waveband, metallicity, the degree of heat redistribution, and the possible presence of thermal inversions and find a rich diversity of behaviors. Measurements of transiting extrasolar giant planets (EGPs) at short wavelengths by MOST, Kepler, and CoRoT, as well as by proposed dedicated multi-band missions, can complement measurements in the near- and mid-IR using {\it Spitzer} and JWST.
Collectively, such measurements can help determine metallicity, compositions, atmospheric temperatures, and the cause of thermal inversions (when they arise) for EGPs with a broad range of radii, masses, degrees of stellar insolation, and ages. With this paper, we reappraise and highlight the diagnostic potential of albedo measurements of hot EGPs shortward of $\sim$1.3 $\mu$m.
Comments: 6 pages, 1 table, 1 color figure; submitted to the Astrophysical Journal
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0803.2523v1 [astro-ph]
Submission history
From: Adam Burrows [view email]
[v1] Mon, 17 Mar 2008 20:23:15 GMT (57kb)
http://arxiv.org/abs/0803.2523
TiO and VO broad band absorption features in the optical spectrum of the atmosphere of the hot-Jupiter HD209458b
Authors: J.-M. Desert, A. Vidal-Madjar, A. Lecavelier des Etangs, D. Sing, D. Ehrenreich, G. Hebrard, R. Ferlet
(Submitted on 10 Sep 2008)
Abstract: The presence of titanium oxide (TiO) and vanadium oxide (VO) gas phase species is searched for in the atmosphere of the hot Jupiter HD209458b. We compared a model for the planets transmitted spectrum to multi-wavelength eclipse-depth measurements (from 3000 to 10000 Angstrom), obtained by Sing et al. (2008a) using archived HST-STIS time series spectra.
We make use of these observations to search for spectral signatures from extra absorbers in the planet atmosphere between 6000 and 8000 Angstrom. Along with sodium depletion and Rayleigh scattering recently published for this exoplanet atmosphere, an extra absorber of uncertain origin, redward of the sodium lines, resides in the atmosphere of the planet. Furthermore, this planet has a stratosphere experiencing a thermal inversion caused by the capture of optical stellar flux by absorbers that resides at altitude.
Recent models have predicted that the presence of TiO and VO in the atmosphere of HD209458b may be responsible for this temperature inversion. Although no specific TiO and VO spectral band head signatures have been identified unambiguously in the observed spectrum, we suggest here that the opacities of those molecules are possible candidates to explain the remaining continuous broad band absorption observed between 6200 and 8000 Angstrom.
To match reasonably well the data, the abundances of TiO and VO molecules are evaluated from ten to one thousand times below solar. This upper limit result is in agreement with expected variations with altitude due to depletion effects such as condensation.
Comments: 9 pages, 4 figures. Accepted for publication in Astronomy & Astrophysics
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0809.1865v1 [astro-ph]
Submission history
From: Jean-Michel D\’esert [view email]
[v1] Wed, 10 Sep 2008 20:25:26 GMT (56kb)
http://arxiv.org/abs/0809.1865
Three Dimensional Modeling of Hot Jupiter Atmospheric Flows
Authors: Emily Rauscher, Kristen Menou (Columbia)
(Submitted on 15 Jul 2009)
Abstract: We present a three dimensional hot Jupiter model, extending from 200 bar to 1 mbar, using the Intermediate General Circulation Model from the University of Reading. Our horizontal spectral resolution is T31 (equivalent to a grid of 48×96), with 33 logarithmically spaced vertical levels. A simplified (Newtonian) scheme is employed for the radiative forcing.
We adopt a physical set up nearly identical to the model of HD 209458b by Cooper & Showman (2005,2006) to facilitate a direct model inter-comparison. Our results are broadly consistent with theirs but significant differences also emerge. The atmospheric flow is characterized by a super-rotating equatorial jet, transonic wind speeds, and eastward advection of heat away from the dayside. We identify a dynamically-induced temperature inversion (“stratosphere”) on the planetary dayside and find that temperatures at the planetary limb differ systematically from local radiative equilibrium values, a potential source of bias for transit spectroscopic interpretations.
While our model atmosphere is quasi-identical to that of Cooper & Showman (2005,2006) and we solve the same meteorological equations, we use different algorithmic methods, spectral-implicit vs. grid-explicit, which are known to yield fully consistent results in the Earth modeling context. The model discrepancies identified here indicate that one or both numerical methods do not faithfully capture all of the atmospheric dynamics at work in the hot Jupiter context.
We highlight the emergence of a shock-like feature in our model, much like that reported recently by Showman et al. (2009), and suggest that improved representations of energy conservation may be needed in hot Jupiter atmospheric models, as emphasized by Goodman (2009).
Comments: 25 pages, 6 figures, submitted to ApJ, version with hi-res figures: this http URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:0907.2692v1 [astro-ph.EP]
Submission history
From: Emily Rauscher [view email]
[v1] Wed, 15 Jul 2009 20:03:39 GMT (694kb,D)
http://arxiv.org/abs/0907.2692
Water in HD 209458b’s atmosphere from 3.6 – 8 microns IRAC photometric observations in primary transit
Authors: J.P. Beaulieu, D.M. Kipping, V. Batista, G. Tinetti, I. Ribas, S. Carey, J. A. Noriega-Crespo, C. A. Griffith, G. Campanella, S. Dong, J. Tennyson, R.J. Barber, P. Deroo, S.J. Fossey, D. Liang, M. R. Swain, Y.
Yung, N. Allard
(Submitted on 1 Sep 2009)
Abstract: The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5, 5.8 and 8.0 microns using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope.
We detail here the procedures we adopted to correct for the systematic trends present in the IRAC data. The light curves were fitted including limb darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, finding almost identical results. The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 3.6 microns, 1.469 +- 0.013 % and 1.448 +- 0.013 %; at 4.5 microns, 1.478 +- 0.017 % ; at 5.8 microns, 1.549 +- 0.015 % and at 8.0 microns 1.535 +- 0.011 %.
Our results clearly indicate the presence of water in the planetary atmosphere. Our broad band photometric measurements with IRAC prevent us from determining the additional presence of other other molecules such as CO, CO2 and methane for which spectroscopy is needed.
While water vapour with a mixing ratio of 10^-4-10^-3 combined with thermal profiles retrieved from the day-side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile.
Comments: 13 pages, 6 tables, 8 figures, MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:0909.0185v1 [astro-ph.EP]
Submission history
From: Jean-Philippe Beaulieu [view email]
[v1] Tue, 1 Sep 2009 13:55:39 GMT (1030kb)
http://arxiv.org/abs/0909.0185