96 research outputs found
Updating quasar bolometric luminosity corrections. II. Infrared bolometric corrections
We present infrared bolometric luminosity corrections derived from the
detailed spectral energy distributions of 62 bright quasars of low- to
moderate-redshift (z=0.03-1.4). At 1.5, 2, 3, 7, 12, 15, and 24 microns we
provide bolometric corrections of the mathematical forms L_iso=\zeta \lambda
L_\lambda and log(L_iso)=A+B log(\lambda L_\lambda). Bolometric corrections for
radio-loud and radio-quiet objects are consistent within 95% confidence
intervals, so we do not separate them. Bolometric luminosities estimated using
these corrections are typically smaller than those derived from some commonly
used in the literature. We investigate the possibility of a luminosity
dependent bolometric correction and find that, while the data are consistent
with such a correction, the dispersion is too large and the luminosity range
too small to warrant such a detailed interpretation. Bolometric corrections at
1.5 m are appropriate for objects with properties that fall in the range
log(L_bol)=45.4-47.3 and bolometric corrections at all other wavelengths are
appropriate for objects with properties that fall in the range
log(L_bol)=45.1-47.0.Comment: 13 pages, 4 tables, 8 figures, accepted to MNRA
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.Comment: 21 pages, 8 figures, accepted by the Astrophysical Journa
Revisiting the HIP 41378 System with K2 and Spitzer
We present new observations of the multiplanet system HIP 41378, a bright star (V = 8.9, K s = 7.7) with five known transiting planets. Previous K2 observations showed multiple transits of two Neptune-sized bodies and single transits of three larger planets (R P = 0.33R J , 0.47R J , 0.88R J ). K2 recently observed the system again in Campaign 18 (C18). We observe one new transit each of two of the larger planets d/f, giving maximal orbital periods of 1114/1084 days, as well as integer divisions of these values down to a lower limit of about 50 days. We use all available photometry to determine the eccentricity distributions of HIP 41378 d & f, finding that periods lesssim300 days require non-zero eccentricity. We check for overlapping orbits of planets d and f to constrain their mutual periods, finding that short periods (P < 300 days) for planet f are disfavored. We also observe transits of planets b and c with Spitzer/Infrared Array Camera (IRAC), which we combine with the K2 observations to search for transit timing variations (TTVs). We find a linear ephemeris for planet b, but see a significant TTV signal for planet c. The ability to recover the two smaller planets with Spitzer shows that this fascinating system will continue to be detectable with Spitzer, CHEOPS, TESS, and other observatories, allowing us to precisely determine the periods of d and f, characterize the TTVs of planet c, recover the transits of planet e, and further enhance our view of this remarkable dynamical laboratory
An Improved Transit Measurement for a 2.4 R⊕ Planet Orbiting A Bright Mid-M Dwarf K2–28
We present a new Spitzer transit observation of K2–28b, a sub-Neptune (Rp = 2.45 ± 0.28 R⊕) orbiting a relatively bright (V_(mag) = 16.06, K_(mag) = 10.75) metal-rich M4 dwarf (EPIC 206318379). This star is one of only seven with masses less than 0.2 M⊙ known to host transiting planets, and the planet appears to be a slightly smaller analogue of GJ 1214b (2.85 ± 0.20 R⊕). Our new Spitzerobservations were taken two years after the original K2 discovery data and have a significantly higher cadence, allowing us to derive improved estimates for this planet's radius, semimajor axis, and orbital period, which greatly reduce the uncertainty in the prediction of near future transit times for the James Webb Space Telescope (JWST) observations. We also evaluate the system's suitability for atmospheric characterization with JWST and find that it is currently the only small (<3 R⊕) and cool (<600 K) planet aside from GJ 1214b with a potentially detectable secondary eclipse. We also note that this system is a favorable target for near-infrared radial velocity instruments on larger telescopes (e.g., the Habitable Planet Finder on the Hobby–Eberly Telescope), making it one of only a handful of small, cool planets accessible with this technique. Finally, we compare our results with the simulated catalog of the Transiting Exoplanet Survey Satellite (TESS) and find K2–28b to be representative of the kind of mid-M systems that should be detectable in the TESS sample
A Spitzer Transmission Spectrum for the Exoplanet GJ 436b, Evidence for Stellar Variability, and Constraints on Dayside Flux Variations
In this paper we describe a uniform analysis of eight transits and eleven
secondary eclipses of the extrasolar planet GJ 436b obtained in the 3.6, 4.5,
and 8.0 micron bands using the IRAC instrument on the Spitzer Space Telescope
between UT 2007 June 29 and UT 2009 Feb 4. We find that the best-fit transit
depths for visits in the same bandpass can vary by as much as 8% of the total
(4.7 sigma significance) from one epoch to the next. Although we cannot
entirely rule out residual detector effects or a time-varying, high-altitude
cloud layer in the planet's atmosphere as the cause of these variations, we
consider the occultation of active regions on the star in a subset of the
transit observations to be the most likely explanation. We reconcile the
presence of magnetically active regions with the lack of significant visible or
infrared flux variations from the star by proposing that the star's spin axis
is tilted with respect to our line of sight, and that the planet's orbit is
therefore likely to be misaligned. These observations serve to illustrate the
challenges associated with transmission spectroscopy of planets orbiting
late-type stars; we expect that other systems, such as GJ 1214, may display
comparably variable transit depths. Our measured 8 micron secondary eclipse
depths are consistent with a constant value, and we place a 1 sigma upper limit
of 17% on changes in the planet's dayside flux in this band. Averaging over the
eleven visits gives us an improved estimate of 0.0452% +/- 0.0027% for the
secondary eclipse depth. We combine timing information from our observations
with previously published data to produce a refined orbital ephemeris, and
determine that the best-fit transit and eclipse times are consistent with a
constant orbital period. [ABRIDGED]Comment: 26 pages, 18 figures, 7 tables in emulateapj format. Accepted for
publication in Ap
The New Generation Atlas of Quasar Spectral Energy Distributions from Radio to X-rays
We have produced the next generation of quasar spectral energy distributions
(SEDs), essentially updating the work of Elvis et al. (1994) by using
high-quality data obtained with several space and ground-based telescopes,
including NASA's Great Observatories. We present an atlas of SEDs of 85
optically bright, non-blazar quasars over the electromagnetic spectrum from
radio to X-rays. The heterogeneous sample includes 27 radio-quiet and 58
radio-loud quasars. Most objects have quasi-simultaneous ultraviolet-optical
spectroscopic data, supplemented with some far-ultraviolet spectra, and more
than half also have Spitzer mid-infrared IRS spectra. The X-ray spectral
parameters are collected from the literature where available. The radio,
far-infrared, and near-infrared photometric data are also obtained from either
the literature or new observations. We construct composite spectral energy
distributions for radio-loud and radio-quiet objects and compare these to those
of Elvis et al., finding that ours have similar overall shapes, but our
improved spectral resolution reveals more detailed features, especially in the
mid and near-infrared.Comment: 46 pages, 10 figures, 10 tables, Accepted by ApJS. Composite SED data
files for radio-loud and radio-quiet quasars (rlmsedMR.txt, rqmsedMR.txt) are
included in the source (Other formats -> Source). Supplemental figures are
not include
WASP-107b’s Density Is Even Lower: A Case Study for the Physics of Planetary Gas Envelope Accretion and Orbital Migration
With a mass in the Neptune regime and a radius of Jupiter, WASP-107b presents a challenge to planet formation theories. Meanwhile, the planet's low surface gravity and the star's brightness also make it one of the most favorable targets for atmospheric characterization. Here, we present the results of an extensive 4 yr Keck/HIRES radial-velocity (RV) follow-up program of the WASP-107 system and provide a detailed study of the physics governing the accretion of the gas envelope of WASP-107b. We reveal that WASP-107b's mass is only 1.8 Neptune masses (M_b = 30.5 ± 1.7 M_⊕). The resulting extraordinarily low density suggests that WASP-107b has a H/He envelope mass fraction of >85% unless it is substantially inflated. The corresponding core mass of <4.6 M_⊕ at 3σ is significantly lower than what is traditionally assumed to be necessary to trigger massive gas envelope accretion. We demonstrate that this large gas-to-core mass ratio most plausibly results from the onset of accretion at gsim1 au onto a low-opacity, dust-free atmosphere and subsequent migration to the present-day a_b = 0.0566 ± 0.0017 au. Beyond WASP-107b, we also detect a second, more massive planet (M_c sin i = 0.36 ± 0.04MJ ) on a wide eccentric orbit (e _c = 0.28 ± 0.07) that may have influenced the orbital migration and spin–orbit misalignment of WASP-107b. Overall, our new RV observations and envelope accretion modeling provide crucial insights into the intriguing nature of WASP-107b and the system's formation history. Looking ahead, WASP-107b will be a keystone planet to understand the physics of gas envelope accretion
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