194 research outputs found
HATNet Field G205: Follow-Up Observations of 28 Transiting-Planet candidates and Confirmation of the Planet HAT-P-8b
We report the identification of 32 transiting-planet candidates in HATNet
field G205. We describe the procedures that we have used to follow up these
candidates with spectroscopic and photometric observations, and we present a
status report on our interpretation of the 28 candidates for which we have
follow-up observations. Eight are eclipsing binaries with orbital solutions
whose periods are consistent with their photometric ephemerides; two of these
spectroscopic orbits are singled-lined and six are double-lined. For one of the
candidates, a nearby but fainter eclipsing binary proved to be the source for
the HATNet light curve, due to blending in the HATNet images. Four of the
candidates were found to be rotating more rapidly than vsini = 50 km/s and were
not pursued further. Thirteen of the candidates showed no significant velocity
variation at the level of 0.5 to 1.0 km/s . Seven of these were eventually
withdrawn as photometric false alarms based on an independent reanalysis using
more sophisticated tools. Of the remaining six, one was put aside because a
close visual companion proved to be a spectroscopic binary, and two were not
followed up because the host stars were judged to be too large. Two of the
remaining candidates are members of a visual binary, one of which was
previously confirmed as the first HATNet transiting planet, HAT-P-1b. In this
paper we confirm that the last of this set of candidates is also a a transiting
planet, which we designate HAT-P-8b, with mass Mp = 1.52 +/- 0.18/0.16 Mjup,
radius Rp = 1.50 +/- 0.08/0.06 Rjup, and photometric period P = 3.076320 +/-
0.000004 days. HAT-P-8b has an inflated radius for its mass, and a large mass
for its period. The host star is a solar-metallicity F dwarf, with mass M* =
1.28 +/- 0.04 Msun and Rp = 1.58 +/- 0.08/0.06 Rsun.Comment: 16 pages, 6 figures, 13 table
Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
We report the distribution of planets as a function of planet radius (R_p),
orbital period (P), and stellar effective temperature (Teff) for P < 50 day
orbits around GK stars. These results are based on the 1,235 planets (formally
"planet candidates") from the Kepler mission that include a nearly complete set
of detected planets as small as 2 Earth radii (Re). For each of the 156,000
target stars we assess the detectability of planets as a function of R_p and P.
We also correct for the geometric probability of transit, R*/a. We consider
first stars within the "solar subset" having Teff = 4100-6100 K, logg =
4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having
noise low enough to permit detection of planets down to 2 Re. We count planets
in small domains of R_p and P and divide by the included target stars to
calculate planet occurrence in each domain. Occurrence of planets varies by
more than three orders of magnitude and increases substantially down to the
smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25
AU) in our study. For P < 50 days, the radius distribution is given by a power
law, df/dlogR= k R^\alpha. This rapid increase in planet occurrence with
decreasing planet size agrees with core-accretion, but disagrees with
population synthesis models. We fit occurrence as a function of P to a power
law model with an exponential cutoff below a critical period P_0. For smaller
planets, P_0 has larger values, suggesting that the "parking distance" for
migrating planets moves outward with decreasing planet size. We also measured
planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The
occurrence of 2-4 Re planets in the Kepler field increases with decreasing
Teff, making these small planets seven times more abundant around cool stars
than the hottest stars in our sample. [abridged]Comment: Submitted to ApJ, 22 pages, 10 figure
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
TOI-3235 b: a transiting giant planet around an M4 dwarf star
We present the discovery of TOI-3235 b, a short-period Jupiter orbiting an
M-dwarf with a stellar mass close to the critical mass at which stars
transition from partially to fully convective. TOI-3235 b was first identified
as a candidate from TESS photometry, and confirmed with radial velocities from
ESPRESSO, and ground-based photometry from HATSouth, MEarth-South,
TRAPPIST-South, LCOGT, and ExTrA. We find that the planet has a mass of
and a radius of . It
orbits close to its host star, with an orbital period of ,
but has an equilibrium temperature of , well below
the expected threshold for radius inflation of hot Jupiters. The host star has
a mass of , a radius of
, an effective temperature of , and a J-band magnitude of . Current planet
formation models do not predict the existence of gas giants such as TOI-3235 b
around such low-mass stars. With a high transmission spectroscopy metric,
TOI-3235 b is one of the best-suited giants orbiting M-dwarfs for atmospheric
characterization.Comment: 15 pages, 4 figures. Accepted for publication in APJ
CfA4: Light Curves for 94 Type Ia Supernovae
We present multi-band optical photometry of 94 spectroscopically-confirmed
Type Ia supernovae (SN Ia) in the redshift range 0.0055 to 0.073, obtained
between 2006 and 2011. There are a total of 5522 light curve points. We show
that our natural system SN photometry has a precision of roughly 0.03 mag or
better in BVr'i', 0.06 mag in u', and 0.07 mag in U for points brighter than
17.5 mag and estimate that it has a systematic uncertainty of 0.014, 0.010,
0.012, 0.014, 0.046, and 0.073 mag in BVr'i'u'U, respectively. Comparisons of
our standard system photometry with published SN Ia light curves and comparison
stars reveal mean agreement across samples in the range of ~0.00-0.03 mag. We
discuss the recent measurements of our telescope-plus-detector throughput by
direct monochromatic illumination by Cramer et al (in prep.). This technique
measures the whole optical path through the telescope, auxiliary optics,
filters, and detector under the same conditions used to make SN measurements.
Extremely well-characterized natural-system passbands (both in wavelength and
over time) are crucial for the next generation of SN Ia photometry to reach the
0.01 mag accuracy level. The current sample of low-z SN Ia is now sufficiently
large to remove most of the statistical sampling error from the dark energy
error budget. But pursuing the dark-energy systematic errors by determining
highly-accurate detector passbands, combining optical and near-infrared (NIR)
photometry and spectra, using the nearby sample to illuminate the population
properties of SN Ia, and measuring the local departures from the Hubble flow
will benefit from larger, carefully measured nearby samples.Comment: 43 page
Optimal Timing and Legal Decisionmaking: The Case of the Liquidation Decision in Bankruptcy
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