It is likely that, in the next several years, the Corot and Kepler satellites will find many terr... more It is likely that, in the next several years, the Corot and Kepler satellites will find many terrestrial planets around other stars. In order to judge what fraction of these planets are likely to be hospitable to life, it is important to reassess the notion of the habitable zone. Classical considerations of habitability, in the context of extrasolar planets, have
ABSTRACT The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morpholog... more ABSTRACT The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological structures that can be interpreted as being due to dynamical influence from unseen giant planets residing in the systems. At the ages of the systems of a few hundred Myrs, such planets are expected to have cooled down to temperatures of ~200 K, which makes them unreachable from the ground due to their faintness at JHKL wavelengths and the prohibitively large thermal background at longer wavelengths. Spitzer, however, has the sensitivity required at 4.5 micron to detect such objects. As we have shown previously (Janson et al. 2012), a dedicated observing strategy and data reduction scheme can be used to improve the Spitzer contrast performance by more than an order of magnitude compared to conventional methods, which enables this degree of sensitivity down to separations of ~10'. The corresponding detection space provides an excellent match to the predicted properties of inferred companions in the three systems. Here, we propose to re-observe Fomalhaut to follow up a candidate companion detected in our previous image, and to observe Vega and Eps Eri to search for their inferred companions. In each case we will be sensitive to Jovian or sub-Jovian companions in the primary separation regions of interest, which is a factor 3 better mass sensitivity than previously achieved. These observations provide a unique opportunity to study far colder and more Jupiter-like planets than previously imaged.
The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCA... more The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of the cosmic microwave background and Galactic and extra-Galactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes a double-nulled design where emission from the sky is compared to that from an external cryogenic full-aperture blackbody calibrator by cryogenic switching radiometers containing internal blackbody reference loads. In order to further minimize sources of systematic error, ARCADE 2 features a cold fully open aperture with all radiometrically active components maintained at near 2.7 K without windows or other warm objects, achieved through a novel thermal design. We discuss the design and performance of the ARCADE 2 instrument in its 2005 and 2006 flights. Subject headings: instrumentation: detectors – cosmic microwave background – radio continuum: galaxies 1.
It is likely that, in the next several years, the Corot and Kepler satellites will find many terr... more It is likely that, in the next several years, the Corot and Kepler satellites will find many terrestrial planets around other stars. In order to judge what fraction of these planets are likely to be hospitable to life, it is important to reassess the notion of the habitable zone. Classical considerations of habitability, in the context of extrasolar planets, have often regarded it as a binary property (either a planet is or is not habitable). But according to the standard liquid water definition, the Earth itself is only partially habitable. I will describe a way to use energy balance climate models to assess the spatial and temporal habitability of terrestrial planets that are not too different from the Earth. Initial investigations of model planets' temperature distributions indicate that climate varies with observable features of planets (e.g., how far they are from their star) and unobservable features (e.g., how fast they are spinning, how much surface water they have, what...
An investigation is made into the three-dimensional structure of wind and temperature in Jovian v... more An investigation is made into the three-dimensional structure of wind and temperature in Jovian vortices. Through the thermal wind equation, vertical wind gradients are related to horizontal temperature gradients. We derive the thermal wind equation including the cyclostrophic term. We posit a similarity model for the horizontal-vertical structure of potential temperature in a vortex. In this model, the thermal wind equation may be solved for the case of concentric, homeccentric, elliptical streamlines coincident with isotachs. The solution is seen to give a separable horizontal-vertical structure in the geostrophic and cyclostrophic limits, but not in between. The case where eccentricity is neither zero nor unity is seen to be problematic, however, because the flow then implies non-vanishing divergence. This formal solution is applied to two vortices on Jupiter – the Great Red Spot and the White Oval BC. Radial-vertical sections of isotachs, angular momentum, potential temperature,...
Time-series photometry of the new transient in Cassiopeia (GSC 3656-1328, see CBET #711) during N... more Time-series photometry of the new transient in Cassiopeia (GSC 3656-1328, see CBET #711) during November 1-10 with the telescopes of the Center for Backyard Astrophysics (CBA) reveals no variability other than the timescale of overall decay.
Proceedings of the National Academy of Sciences of the United States of America, Jan 16, 2014
The goal of finding and characterizing nearby Earth-like planets is driving many NASA high-contra... more The goal of finding and characterizing nearby Earth-like planets is driving many NASA high-contrast flagship mission concepts, the latest of which is known as the Advanced Technology Large-Aperture Space Telescope (ATLAST). In this article, we calculate the optimal spectral resolution R = λ/δλ and minimum signal-to-noise ratio per spectral bin (SNR), two central design requirements for a high-contrast space mission, to detect signatures of water, oxygen, and chlorophyll on an Earth twin. We first develop a minimally parametric model and demonstrate its ability to fit synthetic and observed Earth spectra; this allows us to measure the statistical evidence for each component's presence. We find that water is the easiest to detect, requiring a resolution R ≳ 20, while the optimal resolution for oxygen is likely to be closer to R = 150, somewhat higher than the canonical value in the literature. At these resolutions, detecting oxygen will require approximately two times the SNR as w...
MAH calculates the posterior distribution of the "minimum atmospheric height" (MAH) of ... more MAH calculates the posterior distribution of the "minimum atmospheric height" (MAH) of an exoplanet by inputting the joint posterior distribution of the mass and radius. The code collapses the two dimensions of mass and radius into a one dimensional term that most directly speaks to whether the planet has an atmosphere or not. The joint mass-radius posteriors derived from a fit of some exoplanet data (likely using MCMC) can be used by MAH to evaluate the posterior distribution of R_MAH, from which the significance of a non-zero R_MAH (i.e. an atmosphere is present) is calculated.
We explore the influences on gas-giant radius evolution of both the initial heat content and of a... more We explore the influences on gas-giant radius evolution of both the initial heat content and of a variety of types of thermal processes in the atmosphere and the deep interior. In particular, we compare the radius-expansion effects of atmospheric and deep-interior heating at the same power levels and derive the power required to achieve a given radius increase when night-side cooling is incorporated. We find that models that include consistent day/night cooling are more similar to isotropically irradiated models when there is more heat redistributed from the dayside to the nightside, and that, when taking night-side cooling into account, it might be impossible to explain the radii of very highly inflated hot Jupiters without invoking extra power sources in the deep interior.
The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological stru... more The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological structures that can be interpreted as being due to dynamical influence from unseen giant planets residing in the systems. At the ages of the systems of a few hundred Myrs, such planets are expected to have cooled down to temperatures of ~200 K, which makes them unreachable from the ground due to their faintness at JHKL wavelengths and the prohibitively large thermal background at longer wavelengths. Spitzer, however, has the sensitivity required at 4.5 micron to detect such objects. As we have shown previously (Janson et al. 2012), a dedicated observing strategy and data reduction scheme can be used to improve the Spitzer contrast performance by more than an order of magnitude compared to conventional methods, which enables this degree of sensitivity down to separations of ~10'. The corresponding detection space provides an excellent match to the predicted properties of inferred companio...
We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 2... more We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars observed by HiCIAO on the Subaru Telescope, NIRI on Gemini North, and NICI on Gemini South. The stars cover a wide range of ages and spectral types, and include five detections (kap And b, two ~60 M_J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722 B). We conduct a uniform, Bayesian analysis of the ages of our entire sample, using both membership in a kinematic moving group and activity/rotation age indicators, to obtain posterior age distributions. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis beyond which the distribution function for radial-velocity planets cannot extend, finding model-dependent values of ~30--100 AU. Finally...
This white paper discusses a repurposed mission for the Kepler spacecraft that focusses on solvin... more This white paper discusses a repurposed mission for the Kepler spacecraft that focusses on solving outstanding problems in planet formation and evolution by targeting the study of the hot Jupiter population of young stars. This mission can solve the question of the mode of migration of hot Jupiters, address the problem of whether Jupiters form by hot-start (gravitational instability) or cold-start (core accretion) mechanisms, and provide a wealth of data on the early stages of planetary system evolution during the active phases of stars which impact planetary habitability. In one year of observations of three weeks dwell time per field, Kepler would increase by more than an order of magnitude the number of known hot Jupiters, which can be followed up with fast cadence observations to to search for transit timing variations and to perform asteroseismological characterization of the host stars. This mission scenario continues to operate Kepler in the photometric monitoring mode for wh...
It is likely that, in the next several years, the Corot and Kepler satellites will find many terr... more It is likely that, in the next several years, the Corot and Kepler satellites will find many terrestrial planets around other stars. In order to judge what fraction of these planets are likely to be hospitable to life, it is important to reassess the notion of the habitable zone. Classical considerations of habitability, in the context of extrasolar planets, have
ABSTRACT The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morpholog... more ABSTRACT The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological structures that can be interpreted as being due to dynamical influence from unseen giant planets residing in the systems. At the ages of the systems of a few hundred Myrs, such planets are expected to have cooled down to temperatures of ~200 K, which makes them unreachable from the ground due to their faintness at JHKL wavelengths and the prohibitively large thermal background at longer wavelengths. Spitzer, however, has the sensitivity required at 4.5 micron to detect such objects. As we have shown previously (Janson et al. 2012), a dedicated observing strategy and data reduction scheme can be used to improve the Spitzer contrast performance by more than an order of magnitude compared to conventional methods, which enables this degree of sensitivity down to separations of ~10'. The corresponding detection space provides an excellent match to the predicted properties of inferred companions in the three systems. Here, we propose to re-observe Fomalhaut to follow up a candidate companion detected in our previous image, and to observe Vega and Eps Eri to search for their inferred companions. In each case we will be sensitive to Jovian or sub-Jovian companions in the primary separation regions of interest, which is a factor 3 better mass sensitivity than previously achieved. These observations provide a unique opportunity to study far colder and more Jupiter-like planets than previously imaged.
The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCA... more The second generation Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) instrument is a balloon-borne experiment to measure the radiometric temperature of the cosmic microwave background and Galactic and extra-Galactic emission at six frequencies from 3 to 90 GHz. ARCADE 2 utilizes a double-nulled design where emission from the sky is compared to that from an external cryogenic full-aperture blackbody calibrator by cryogenic switching radiometers containing internal blackbody reference loads. In order to further minimize sources of systematic error, ARCADE 2 features a cold fully open aperture with all radiometrically active components maintained at near 2.7 K without windows or other warm objects, achieved through a novel thermal design. We discuss the design and performance of the ARCADE 2 instrument in its 2005 and 2006 flights. Subject headings: instrumentation: detectors – cosmic microwave background – radio continuum: galaxies 1.
It is likely that, in the next several years, the Corot and Kepler satellites will find many terr... more It is likely that, in the next several years, the Corot and Kepler satellites will find many terrestrial planets around other stars. In order to judge what fraction of these planets are likely to be hospitable to life, it is important to reassess the notion of the habitable zone. Classical considerations of habitability, in the context of extrasolar planets, have often regarded it as a binary property (either a planet is or is not habitable). But according to the standard liquid water definition, the Earth itself is only partially habitable. I will describe a way to use energy balance climate models to assess the spatial and temporal habitability of terrestrial planets that are not too different from the Earth. Initial investigations of model planets' temperature distributions indicate that climate varies with observable features of planets (e.g., how far they are from their star) and unobservable features (e.g., how fast they are spinning, how much surface water they have, what...
An investigation is made into the three-dimensional structure of wind and temperature in Jovian v... more An investigation is made into the three-dimensional structure of wind and temperature in Jovian vortices. Through the thermal wind equation, vertical wind gradients are related to horizontal temperature gradients. We derive the thermal wind equation including the cyclostrophic term. We posit a similarity model for the horizontal-vertical structure of potential temperature in a vortex. In this model, the thermal wind equation may be solved for the case of concentric, homeccentric, elliptical streamlines coincident with isotachs. The solution is seen to give a separable horizontal-vertical structure in the geostrophic and cyclostrophic limits, but not in between. The case where eccentricity is neither zero nor unity is seen to be problematic, however, because the flow then implies non-vanishing divergence. This formal solution is applied to two vortices on Jupiter – the Great Red Spot and the White Oval BC. Radial-vertical sections of isotachs, angular momentum, potential temperature,...
Time-series photometry of the new transient in Cassiopeia (GSC 3656-1328, see CBET #711) during N... more Time-series photometry of the new transient in Cassiopeia (GSC 3656-1328, see CBET #711) during November 1-10 with the telescopes of the Center for Backyard Astrophysics (CBA) reveals no variability other than the timescale of overall decay.
Proceedings of the National Academy of Sciences of the United States of America, Jan 16, 2014
The goal of finding and characterizing nearby Earth-like planets is driving many NASA high-contra... more The goal of finding and characterizing nearby Earth-like planets is driving many NASA high-contrast flagship mission concepts, the latest of which is known as the Advanced Technology Large-Aperture Space Telescope (ATLAST). In this article, we calculate the optimal spectral resolution R = λ/δλ and minimum signal-to-noise ratio per spectral bin (SNR), two central design requirements for a high-contrast space mission, to detect signatures of water, oxygen, and chlorophyll on an Earth twin. We first develop a minimally parametric model and demonstrate its ability to fit synthetic and observed Earth spectra; this allows us to measure the statistical evidence for each component's presence. We find that water is the easiest to detect, requiring a resolution R ≳ 20, while the optimal resolution for oxygen is likely to be closer to R = 150, somewhat higher than the canonical value in the literature. At these resolutions, detecting oxygen will require approximately two times the SNR as w...
MAH calculates the posterior distribution of the "minimum atmospheric height" (MAH) of ... more MAH calculates the posterior distribution of the "minimum atmospheric height" (MAH) of an exoplanet by inputting the joint posterior distribution of the mass and radius. The code collapses the two dimensions of mass and radius into a one dimensional term that most directly speaks to whether the planet has an atmosphere or not. The joint mass-radius posteriors derived from a fit of some exoplanet data (likely using MCMC) can be used by MAH to evaluate the posterior distribution of R_MAH, from which the significance of a non-zero R_MAH (i.e. an atmosphere is present) is calculated.
We explore the influences on gas-giant radius evolution of both the initial heat content and of a... more We explore the influences on gas-giant radius evolution of both the initial heat content and of a variety of types of thermal processes in the atmosphere and the deep interior. In particular, we compare the radius-expansion effects of atmospheric and deep-interior heating at the same power levels and derive the power required to achieve a given radius increase when night-side cooling is incorporated. We find that models that include consistent day/night cooling are more similar to isotropically irradiated models when there is more heat redistributed from the dayside to the nightside, and that, when taking night-side cooling into account, it might be impossible to explain the radii of very highly inflated hot Jupiters without invoking extra power sources in the deep interior.
The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological stru... more The nearby stars Eps Eri, Vega, and Fomalhaut all host large debris disks with morphological structures that can be interpreted as being due to dynamical influence from unseen giant planets residing in the systems. At the ages of the systems of a few hundred Myrs, such planets are expected to have cooled down to temperatures of ~200 K, which makes them unreachable from the ground due to their faintness at JHKL wavelengths and the prohibitively large thermal background at longer wavelengths. Spitzer, however, has the sensitivity required at 4.5 micron to detect such objects. As we have shown previously (Janson et al. 2012), a dedicated observing strategy and data reduction scheme can be used to improve the Spitzer contrast performance by more than an order of magnitude compared to conventional methods, which enables this degree of sensitivity down to separations of ~10'. The corresponding detection space provides an excellent match to the predicted properties of inferred companio...
We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 2... more We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars observed by HiCIAO on the Subaru Telescope, NIRI on Gemini North, and NICI on Gemini South. The stars cover a wide range of ages and spectral types, and include five detections (kap And b, two ~60 M_J brown dwarf companions in the Pleiades, PZ Tel B, and CD-35 2722 B). We conduct a uniform, Bayesian analysis of the ages of our entire sample, using both membership in a kinematic moving group and activity/rotation age indicators, to obtain posterior age distributions. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis beyond which the distribution function for radial-velocity planets cannot extend, finding model-dependent values of ~30--100 AU. Finally...
This white paper discusses a repurposed mission for the Kepler spacecraft that focusses on solvin... more This white paper discusses a repurposed mission for the Kepler spacecraft that focusses on solving outstanding problems in planet formation and evolution by targeting the study of the hot Jupiter population of young stars. This mission can solve the question of the mode of migration of hot Jupiters, address the problem of whether Jupiters form by hot-start (gravitational instability) or cold-start (core accretion) mechanisms, and provide a wealth of data on the early stages of planetary system evolution during the active phases of stars which impact planetary habitability. In one year of observations of three weeks dwell time per field, Kepler would increase by more than an order of magnitude the number of known hot Jupiters, which can be followed up with fast cadence observations to to search for transit timing variations and to perform asteroseismological characterization of the host stars. This mission scenario continues to operate Kepler in the photometric monitoring mode for wh...
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