arXiv subjects

Drake Deming

Publications and source records attributed to Drake Deming.

At least 163 records · Page 9Linked to original sources

arXiv2010

A Search for Additional Planets in the NASA EPOXI Observations of the Exoplanet System GJ 436

We present time series photometry of the M dwarf transiting exoplanet system GJ 436 obtained with the the EPOCh (Extrasolar Planet Observation and Characterization) component of the NASA EPOXI mission. We conduct a search of the high-precision time series for additional planets around GJ 436, which could be revealed either directly through their photometric transits, or indirectly through the variations these second planets induce on the transits of the previously known planet. In the case of GJ 436, the presence of a second planet is perhaps indicated by the residual orbital eccentricity of the known hot Neptune companion. We find no candidate transits with significance higher than our detection limit. From Monte Carlo tests of the time series, we rule out transiting planets larger than 1.5 R_Earth interior to GJ 436b with 95% confidence, and larger than 1.25 R_Earth with 80% confidence. Assuming coplanarity of additional planets with the orbit of GJ 436b, we cannot expect that putative planets with orbital periods longer than about 3.4 days will transit. However, if such a planet were to transit, we rule out planets larger than 2.0 R_Earth with orbital periods less than 8.5 days with 95% confidence. We also place dynamical constraints on additional bodies in the GJ 436 system. Our analysis should serve as a useful guide for similar analyses for which radial velocity measurements are not available, such as those discovered by the Kepler mission. These dynamical constraints on additional planets with periods from 0.5 to 9 days rule out coplanar secular perturbers as small as 10 M_Earth and non-coplanar secular perturbers as small as 1 M_Earth in orbits close in to GJ 436b. We present refined estimates of the system parameters for GJ 436. We also report a sinusoidal modulation in the GJ 436 light curve that we attribute to star spots. [Abridged]

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arXiv2009

Detection of Planetary Emission from the Exoplanet TrES-2 using Spitzer /IRAC

We present here the results of our observations of TrES-2 using the Infrared Array Camera on Spitzer. We monitored this transiting system during two secondary eclipses, when the planetary emission is blocked by the star. The resulting decrease in flux is 0.127%+-0.021%, 0.230%+-0.024%, 0.199%+-0.054%, and 0.359%+-0.060%, at 3.6 microns, 4.5 microns, 5.8 microns, and 8.0 microns, respectively. We show that three of these flux contrasts are well fit by a black body spectrum with T_{eff}=1500 K, as well as by a more detailed model spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in all four IRAC channels can be explained by models with and without a thermal inversion in the atmosphere of TrES-2, although with different atmospheric chemistry. Based on the assumption of thermochemical equilibrium, the chemical composition of the inversion model seems more plausible, making it a more favorable scenario. TrES-2 also falls in the category of highly irradiated planets which have been theoretically predicted to exhibit thermal inversions. However, more observations at infrared and visible wavelengths would be needed to confirm a thermal inversion in this system. Furthermore, we find that the times of the secondary eclipses are consistent with previously published times of transit and the expectation from a circular orbit. This implies that TrES-2 most likely has a circular orbit, and thus does not obtain additional thermal energy from tidal dissipation of a non-zero orbital eccentricity, a proposed explanation for the large radius of this planet.

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arXiv2009

Studying the atmosphere of the exoplanet HAT-P-7b via secondary eclipse measurements with EPOXI, Spitzer and Kepler

The highly irradiated transiting exoplanet, HAT-P-7b, currently provides one of the best opportunities for studying planetary emission in the optical and infrared wavelengths. We observe six near-consecutive secondary eclipses of HAT-P-7b at optical wavelengths with the EPOXI spacecraft. We place an upper limit on the relative eclipse depth of 0.055% (95% confidence). We also analyze Spitzer observations of the same target in the infrared, obtaining secondary eclipse depths of 0.098+/-0.017%, 0.159+/-0.022%, 0.245+/-0.031% and 0.225+/-0.052% in the 3.6, 4.5, 5.8 and 8.0 micron IRAC bands respectively. We combine these measurements with the recently published Kepler secondary eclipse measurement, and generate atmospheric models for the day-side of the planet that are consistent with both the optical and infrared measurements. The data are best fit by models with a temperature inversion, as expected from the high incident flux. The models predict a low optical albedo of ~< 0.13, with subsolar abundances of Na, K, TiO and VO. We also find that the best fitting models predict that 10% of the absorbed stellar flux is redistributed to the night side of the planet, which is qualitatively consistent with the inefficient day-night redistribution apparent in the Kepler phase curve. Models without thermal inversions fit the data only at the 1.25 sigma level, and also require an overabundance of methane, which is not expected in the very hot atmosphere of HAT-P-7b. We also analyze the eight transits of HAT-P-7b present in the EPOXI dataset and improve the constraints on the system parameters, finding a period of P = 2.2047308+/-0.0000025 days, a stellar radius of R* = 1.824+/-0.089Rsun, a planetary radius of Rp = 1.342+/-0.068RJup and an inclination of i = 85.7+3.5-2.2 deg.

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arXiv2009

The Broadband Infrared Emission Spectrum of the Exoplanet TrES-3

We use the Spitzer Space Telescope to estimate the dayside thermal emission of the exoplanet TrES-3 integrated in the 3.6, 4.5, 5.8, and 8.0 micron bandpasses of the Infrared Array Camera (IRAC) instrument. We observe two secondary eclipses and find relative eclipse depths of 0.00346 +/- 0.00035, 0.00372 +/- 0.00054, 0.00449 +/- 0.00097, and 0.00475 +/- 0.00046, respectively in the 4 IRAC bandpasses. We combine our results with the earlier K band measurement of De Mooij et al. (2009), and compare them with models of the planetary emission. We find that the planet does not require the presence of an inversion layer in the high atmosphere. This is the first very strongly irradiated planet that does not have a temperature inversion, which indicates that stellar or planetary characteristics other than temperature have an important impact on temperature inversion. De Mooij & Snellen (2009) also detected a possible slight offset in the timing of the secondary eclipse in K band. However, based on our 4 Spitzer channels, we place a 3sigma upper limit of |ecos(w)| < 0.0056 where e is the planets orbital eccentricity and w is the longitude of the periastron. This result strongly indicates that the orbit is circular, as expected from tidal circularization theory.

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arXiv2009

Spitzer IRAC Secondary Eclipse Photometry of the Transiting Extrasolar Planet HAT-P-1b

We report Spitzer/IRAC photometry of the transiting giant exoplanet HAT-P-1b during its secondary eclipse. This planet lies near the postulated boundary between the pM and pL-class of hot Jupiters, and is important as a test of models for temperature inversions in hot Jupiter atmospheres. We derive eclipse depths for HAT-P-1b, in units of the stellar flux, that are: 0.080% +/- 0.008%,[3.6um], 0.135% +/- 0.022%,[4.5um],0.203% +/- 0.031%,[5.8um], and $0.238% +/- 0.040%,[8.0um]. These values are best fit using an atmosphere with a modest temperature inversion, intermediate between the archetype inverted atmosphere (HD209458b) and a model without an inversion. The observations also suggest that this planet is radiating a large fraction of the available stellar irradiance on its dayside, with little available for redistribution by circulation. This planet has sometimes been speculated to be inflated by tidal dissipation, based on its large radius in discovery observations, and on a non-zero orbital eccentricity allowed by the radial velocity data. The timing of the secondary eclipse is very sensitive to orbital eccentricity, and we find that the central phase of the eclipse is 0.4999 +/- 0.0005. The difference between the expected and observed phase indicates that the orbit is close to circular, with a 3-sigma limit of |e cosw| < 0.002.

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arXiv2008

Emergent Exoplanet Flux: Review of the Spitzer Results

Observations using the Spitzer Space Telescope provided the first detections of photons from extrasolar planets. Spitzer observations are allowing us to infer the temperature structure, composition, and dynamics of exoplanet atmospheres. The Spitzer studies extend from many hot Jupiters, to the hot Neptune orbiting GJ436. Here I review the current status of Spitzer secondary eclipse observations, and summarize the results from the viewpoint of what is robust, what needs more work, and what the observations are telling us about the physical nature of exoplanet atmospheres.

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arXiv2008

The NASA EPOXI mission of opportunity to gather ultraprecise photometry of known transiting exoplanets

The NASA Discovery mission EPOXI, utilizing the Deep Impact flyby spacecraft, comprises two phases: EPOCh (Extrasolar Planet Observation and Characterization) and DIXI (Deep Impact eXtended Investigation). With EPOCh, we use the 30-cm high resolution visible imager to obtain ultraprecise photometric light curves of known transiting planet systems. We will analyze these data for evidence of additional planets, via transit timing variations or transits; for planetary moons or rings; for detection of secondary eclipses and the constraint of geometric planetary albedos; and for refinement of the system parameters. Over a period of four months, EPOCh observed four known transiting planet systems, with each system observed continuously for several weeks. Here we present an overview of EPOCh, including the spacecraft and science goals, and preliminary photometry results.

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arXiv2008

Preliminary Results on HAT-P-4, TrES-3, XO-2, and GJ 436 from the NASA EPOXI Mission

EPOXI (EPOCh + DIXI) is a NASA Discovery Program Mission of Opportunity using the Deep Impact flyby spacecraft. The EPOCh (Extrasolar Planet Observation and Characterization) Science Investigation will gather photometric time series of known transiting exoplanet systems from January through August 2008. Here we describe the steps in the photometric extraction of the time series and present preliminary results of the first four EPOCh targets.

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arXiv2008

Transits and secondary eclipses of HD 189733 with Spitzer

We present limits on transit timing variations and secondary eclipse depth variations at 8 microns with the Spitzer Space Telescope IRAC camera. Due to the weak limb darkening in the infrared and uninterrupted observing, Spitzer provides the highest accuracy transit times for this bright system, in principle providing sensitivity to secondary planets of Mars mass in resonant orbits. Finally, the transit data provides tighter constraints on the wavelength- dependent atmospheric absorption by the planet.

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arXiv2007

Observations of Extrasolar Planets During the non-Cryogenic Spitzer Space Telescope Mission

Precision infrared photometry from Spitzer has enabled the first direct studies of light from extrasolar planets, via observations at secondary eclipse in transiting systems. Current Spitzer results include the first longitudinal temperature map of an extrasolar planet, and the first spectra of their atmospheres. Spitzer has also measured a temperature and precise radius for the first transiting Neptune-sized exoplanet, and is beginning to make precise transit timing measurements to infer the existence of unseen low mass planets. The lack of stellar limb darkening in the infrared facilitates precise radius and transit timing measurements of transiting planets. Warm Spitzer will be capable of a precise radius measurement for Earth-sized planets transiting nearby M-dwarfs, thereby constraining their bulk composition. It will continue to measure thermal emission at secondary eclipse for transiting hot Jupiters, and be able to distinguish between planets having broad band emission versus absorption spectra. It will also be able to measure the orbital phase variation of thermal emission for close-in planets, even non-transiting planets, and these measurements will be of special interest for planets in eccentric orbits. Warm Spitzer will be a significant complement to Kepler, particularly as regards transit timing in the Kepler field. In addition to studying close-in planets, Warm Spitzer will have significant application in sensitive imaging searches for young planets at relatively large angular separations from their parent stars.

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arXiv2007

Spitzer Transit and Secondary Eclipse Photometry of GJ 436b

We report the results of infrared (8 micron) transit and secondary eclipse photometry of the hot Neptune exoplanet, GJ436b using Spitzer. The nearly photon-limited precision of these data allow us to measure an improved radius for the planet, and to detect the secondary eclipse. The transit (centered at HJD = 2454280.78149 +/-0.00016) shows the flat-bottomed shape typical of infrared transits, and it precisely defines the planet-to-star radius ratio (0.0839 +/-0.0005), independent of the stellar properties. However, we obtain the planetary radius, as well as the stellar mass and radius, by fitting to the transit curve simultaneously with an empirical mass-radius relation for M-dwarfs (M=R). We find Rs=Ms=0.47 +/-0.02 in solar units, and Rp=27,600 +/-1170 km (4.33 +/-0.18 Earth radii). This radius significantly exceeds the radius of a naked ocean planet, and requires a gasesous hydrogen-helium envelope. The secondary eclipse occurs at phase 0.587 +/-0.005, proving a significant orbital eccentricity (e=0.15 +/-0.012). The amplitude of the eclipse (5.7 +/-0.8e-4) indicates a brightness temperature for the planet of T=712 +/-36K. If this is indicative of the planet's physical temperature, it suggests the occurrence of tidal heating in the planet. An uncharacterized second planet likely provides ongoing gravitational perturbations, to maintain GJ436b's orbit eccentricity over long time scales.

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arXiv2007

The Dynamics-Based Approach to Studying Terrestrial Exoplanets

One of the great quests of astronomy is to obtain the spectrum of a terrestrial planet orbiting within the habitable zone of its star, and the dominant challenge in doing so is to isolate the light of the planet from that of the star. Dynamics-based methods separate these signals temporally, whereas imaging techniques do so spatially. In light of the overwhelming dominance of dynamics-based methods over the past decade, we challenge the notion that spectra of terrestrial planets necessarily require extreme imaging methods. We advocate that some resources be committed to refining the proven technologies of radial-velocity measurements, transit photometry, and occultation spectroscopy (i.e. emergent infrared spectra obtained at secondary eclipse). We see a particularly attractive opportunity in M-dwarfs, for which the habitable zone is close to the star, increasing the probability and frequency of transits, and the amplitude of the induced radial-velocity variation. Such planets could be discovered by a dedicated ground-based transit survey of the 10,000 nearest M-dwarfs. The favorable planet-star contrast ratio would make these planets ideal targets for the study of their atmospheres with the technique of occultation spectroscopy.

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arXiv2007

A Ground-Based Search for Thermal Emission from the Exoplanet TrES-1

Eclipsing planetary systems give us an important window on extrasolar planet atmospheres. By measuring the depth of the secondary eclipse, when the planet moves behind the star, we can estimate the strength of the thermal emission from the day side of the planet. Attaining a ground-based detection of one of these eclipses has proven to be a significant challenge, as time-dependent variations in instrument throughput and atmospheric seeing and absorption overwhelm the small signal of the eclipse at infrared wavelengths. We gathered a series of simultaneous L grism spectra of the transiting planet system TrES-1 and a nearby comparison star of comparable brightness, allowing us to correct for these effects in principle. Combining the data from two eclipses, we demonstrate a detection sensitivity of 0.15% in the eclipse depth relative to the stellar flux. This approaches the sensitivity required to detect the planetary emission, which theoretical models predict should lie between 0.05-0.1% of the stellar flux in our 2.9-4.3 micron bandpass. We explore the factors that ultimately limit the precision of this technique, and discuss potential avenues for future improvements.

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arXiv2007

Toward Eclipse Mapping of Hot Jupiters

Recent Spitzer infrared measurements of hot Jupiter eclipses suggest that eclipse mapping techniques could be used to spatially resolve the day-side photospheric emission of these planets using partial occultations. As a first step in this direction, we simulate ingress/egress lightcurves for the three brightest known eclipsing hot Jupiters and evaluate the degree to which parameterized photospheric emission models can be distinguished from each other with repeated, noisy eclipse measurements. We find that the photometric accuracy of Spitzer is insufficient to use this tool effectively. On the other hand, the level of photospheric details that could be probed with a few JWST eclipse measurements could greatly inform hot Jupiter atmospheric modeling efforts. A JWST program focused on non-parametric eclipse map inversions for hot Jupiters should be actively considered.

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arXiv2007

3.8-Micron Photometry During the Secondary Eclipse of the Extrasolar Planet HD 209458b

We report infrared photometry of the extrasolar planet HD 209458b during the time of secondary eclipse (planet passing behind the star). Observations were acquired during two secondary eclipses at the NASA Infrared Telescope Facility (IRTF) in September 2003. We used a circular variable filter (1.5-percent bandpass) centered at 3.8 microns to isolate the predicted flux peak of the planet at this wavelength. Residual telluric absorption and instrument variations were removed by offsetting the telescope to nearby bright comparison stars at a high temporal cadence. Our results give a secondary eclipse depth of 0.0013 +/- 0.0011, not yet sufficient precision to detect the eclipse, whose expected depth is approximately 0.002 - 0.003. We here elucidate the current observational limitations to this technique, and discuss the approach needed to achieve detections of hot Jupiter secondary eclipses at 3.8 microns from the ground.

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arXiv2007

A Spectrum of an Extrasolar Planet

Of the over 200 known extrasolar planets, 14 exhibit transits in front of their parent stars as seen from Earth. Spectroscopic observations of the transiting planets can probe the physical conditions of their atmospheres. One such technique can be used to derive the planetary spectrum by subtracting the stellar spectrum measured during eclipse (planet hidden behind star) from the combined-light spectrum measured outside eclipse (star + planet). Although several attempts have been made from Earth-based observatories, no spectrum has yet been measured for any of the established extrasolar planets. Here we report a measurement of the infrared spectrum (7.5--13.2 micron) of the transiting extrasolar planet HD209458b. Our observations reveal a hot thermal continuum for the planetary spectrum, with approximately constant ratio to the stellar flux over this wavelength range. Superposed on this continuum is a broad emission peak centered near 9.65 micron that we attribute to emission by silicate clouds. We also find a narrow, unidentified emission feature at 7.78 micron. Models of these ``hot Jupiter'' planets predict a flux peak near 10 micron, where thermal emission from the deep atmosphere emerges relatively unimpeded by water absorption, but models dominated by water fit the observed spectrum poorly.

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arXiv2006

A Re-appraisal of the Habitability of Planets Around M Dwarf Stars

Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.

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arXiv2006

A Spitzer Infrared Radius for the Transiting Extrasolar Planet HD209458b

We have measured the infrared transit of the extrasolar planet HD209458b using the Spitzer Space Telescope. We observed two primary eclipse events (one partial and one complete transit) using the 24 micron array of the Multiband Imaging Photometer for Spitzer (MIPS). We analyzed a total of 2392 individual images (10-second integrations) of the planetary system, recorded before, during, and after transit. We perform optimal photometry on the images and use the local zodiacal light as a short-term flux reference. At this long wavelength, the transit curve has a simple box-like shape, allowing robust solutions for the stellar and planetary radii independent of stellar limb darkening, which is negligible at 24 microns. We derive a stellar radius of R$_*$ = 1.06 $\pm$ 0.07 R$_\sun$, a planetary radius of R$_p$ = 1.26 $\pm$ 0.08 R$_J$, and a stellar mass of 1.17 M$_\sun$. Within the errors, our results agree with the measurements at visible wavelengths. The 24-micron radius of the planet therefore does not differ significantly compared to the visible result. We point out the potential for deriving extrasolar transiting planet radii to high accuracy using transit photometry at slightly shorter IR wavelengths where greater photometric precision is possible.

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