333 research outputs found
Spin orbit alignment for KELT-7b and HAT-P-56b via Doppler tomography with TRES
We present Doppler tomographic analyses for the spectroscopic transits of
KELT-7b and HAT-P-56b, two hot-Jupiters orbiting rapidly rotating F-dwarf host
stars. These include analyses of archival TRES observations for KELT-7b, and a
new TRES transit observation of HAT-P-56b. We report spin-orbit aligned
geometries for KELT-7b (2.7 +/- 0.6 deg) and HAT-P-56b (8 +/- 2 deg). The host
stars KELT-7 and HAT-P-56 are among some of the most rapidly rotating
planet-hosting stars known. We examine the tidal re-alignment model for the
evolution of the spin-orbit angle in the context of the spin rates of these
stars. We find no evidence that the rotation rates of KELT-7 and HAT-P-56 have
been modified by star-planet tidal interactions, suggesting that the spin-orbit
angle of systems around these hot stars may represent their primordial
configuration. In fact, KELT-7 and HAT-P-56 are two of three systems in
super-synchronous, spin-orbit aligned states, where the rotation periods of the
host stars are faster than the orbital periods of the planets.Comment: 9 pages, accepted for publication in MNRA
THE Hα EMISSION OF NEARBY M DWARFS AND ITS RELATION TO STELLAR ROTATION
The high-energy emission from low-mass stars is mediated by the magnetic dynamo. Although the mechanisms by which fully convective stars generate large-scale magnetic fields are not well understood, it is clear that, as for solar-type stars, stellar rotation plays a pivotal role. We present 270 new optical spectra of low-mass stars in the Solar Neighborhood. Combining our observations with those from the literature, our sample comprises 2202 measurements or non-detections of Hα emission in nearby M dwarfs. This includes 466 with photometric rotation periods. Stars with masses between 0.1 and 0.6 M[subscript ⊙] are well-represented in our sample, with fast and slow rotators of all masses. We observe a threshold in the mass–period plane that separates active and inactive M dwarfs. The threshold coincides with the fast-period edge of the slowly rotating population, at approximately the rotation period at which an era of rapid rotational evolution appears to cease. The well-defined active/inactive boundary indicates that Hα activity is a useful diagnostic for stellar rotation period, e.g., for target selection for exoplanet surveys, and we present a mass-period relation for inactive M dwarfs. We also find a significant, moderate correlation between L[suscript Hα]/L[subscript bol] and variability amplitude: more active stars display higher levels of photometric variability. Consistent with previous work, our data show that rapid rotators maintain a saturated value of LHα/Lbol. Our data also show a clear power-law decay in L[subscript Hα]/L[subscript bol] with Rossby number for slow rotators, with an index of −1.7 ± 0.1.National Science Foundation (U.S.). Astronomy and Astrophysics Postdoctoral Fellowship (Award AST-1602597
The Redshift of the Optical Transient Associated with GRB 010222
The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the
BeppoSAX satellite. Prompt identification of the associated optical transient
(OT) allowed for spectroscopy with the Tillinghast 1.5m telescope at F. L.
Whipple Observatory while the source was still relatively bright (R ~ 18.6
mag), within five hours of the burst. The OT shows a blue continuum with many
superimposed absorption features corresponding to metal lines at z = 1.477,
1.157, and possibly also at 0.928. The redshift of GRB 010222 is therefore
unambiguously placed at z >= 1.477. The high number of Mg II absorbers and
especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption
lines in the z = 1.477 system further argue either for a very small impact
parameter or that the z = 1.477 system is the GRB host galaxy itself. The
spectral index of the OT is relatively steep, beta = 0.89 +/- 0.03, and this
cannot be caused by dust with a standard Galactic extinction law in the z =
1.477 absorption system. This spectroscopic identification of the redshift of
GRB 010222 shows that prompt and well-coordinated followup of bright GRBs can
be successful even with telescopes of modest aperture.Comment: 12 pages, 3 figures; ApJ Letters accepted version, only minor change
Five Planets Transiting a Ninth Magnitude Star
The Kepler mission has revealed a great diversity of planetary systems and
architectures, but most of the planets discovered by Kepler orbit faint stars.
Using new data from the K2 mission, we present the discovery of a five planet
system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378
is a slightly metal-poor late F-type star with moderate rotation (v sin(i) = 7
km/s) and lies at a distance of 116 +/- 18 from Earth. We find that HIP 41378
hosts two sub-Neptune sized planets orbiting 3.5% outside a 2:1 period
commensurability in 15.6 and 31.7 day orbits. In addition, we detect three
planets which each transit once during the 75 days spanned by K2 observations.
One planet is Neptune sized in a likely ~160 day orbit, one is sub-Saturn sized
likely in a ~130 day orbit, and one is a Jupiter sized planet in a likely ~1
year orbit. We show that these estimates for the orbital periods can be made
more precise by taking into account dynamical stability considerations. We also
calculate the distribution of stellar reflex velocities expected for this
system, and show that it provides a good target for future radial velocity
observations. If a precise orbital period can be determined for the outer
Jovian planet through future observations, it will be an excellent candidate
for follow-up transit observations to study its atmosphere and measure its
oblateness.Comment: Accepted by ApJL. 12 pages, 6 figures, 2 table
Mid-to-Late M Dwarfs Lack Jupiter Analogs
Cold Jovian planets play an important role in sculpting the dynamical
environment in which inner terrestrial planets form. The core accretion model
predicts that giant planets cannot form around low-mass M dwarfs, although this
idea has been challenged by recent planet discoveries. Here, we investigate the
occurrence rate of giant planets around low-mass (0.1-0.3M) M dwarfs.
We monitor a volume-complete, inactive sample of 200 such stars located within
15 parsecs, collecting four high-resolution spectra of each M dwarf over six
years and performing intensive follow-up monitoring of two candidate
radial-velocity variables. We use TRES on the 1.5 m telescope at the Fred
Lawrence Whipple Observatory and CHIRON on the Cerro Tololo Inter-American
Observatory 1.5 m telescope for our primary campaign, and MAROON-X on Gemini
North for high-precision follow-up. We place a 95%-confidence upper limit of
1.5% (68%-confidence limit of 0.57%) on the occurrence of sin1M giant planets out to the water snow line and provide additional
constraints on the giant planet population as a function of sin
and period. Beyond the snow line ( K K), we place
95%-confidence upper limits of 1.5%, 1.7%, and 4.4% (68%-confidence limits of
0.58%, 0.66%, and 1.7%) for 3MsinM,
0.8MsinM, and 0.3MsinM giant planets; i.e., Jupiter analogs are rare around
low-mass M dwarfs. In contrast, surveys of Sun-like stars have found that their
giant planets are most common at these Jupiter-like instellations.Comment: Accepted for publication in AJ; 19 pages, 5 figures, 2 table
LHS 1610A: A Nearby Mid-M Dwarf with a Companion That is Likely A Brown Dwarf
We present the spectroscopic orbit of LHS 1610A, a newly discovered
single-lined spectroscopic binary with a trigonometric distance placing it at
9.9 pm 0.2 pc. We obtained spectra with the TRES instrument on the 1.5m
Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt.
Hopkins in AZ. We demonstrate the use of the TiO molecular bands at 7065 --
7165 Angstroms to measure radial velocities and achieve an average estimated
velocity uncertainty of 28 m/s. We measure the orbital period to be 10.6 days
and calculate a minimum mass of 44.8 pm 3.2 Jupiter masses for the secondary,
indicating that it is likely a brown dwarf. We place an upper limit to 3 sigma
of 2500 K on the effective temperature of the companion from infrared
spectroscopic observations using IGRINS on the 4.3m Discovery Channel
Telescope. In addition, we present a new photometric rotation period of 84.3
days for the primary star using data from the MEarth-South Observatory, with
which we show that the system does not eclipse.Comment: 10 pages, 5 figures; accepted for publication in the Astronomical
Journa
KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-mass Companion Transiting a mid-F Star
We present the discovery of KELT-1b, the first transiting low-mass companion
from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North)
survey. The V=10.7 primary is a mildly evolved, solar-metallicity, mid-F star.
The companion is a low-mass brown dwarf or super-massive planet with mass of
27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period
(P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar
insolation, with an equilibrium temperature assuming zero albedo and perfect
redistribution of 2422 K. Upper limits on the secondary eclipse depth indicate
that either the companion must have a non-zero albedo, or it must experience
some energy redistribution. Comparison with standard evolutionary models for
brown dwarfs suggests that the radius of KELT-1b is significantly inflated.
Adaptive optics imaging reveals a candidate stellar companion to KELT-1, which
is consistent with an M dwarf if bound. The projected spin-orbit alignment
angle is consistent with zero stellar obliquity, and the vsini of the primary
is consistent with tidal synchronization. Given the extreme parameters of the
KELT-1 system, we expect it to provide an important testbed for theories of the
emplacement and evolution of short-period companions, and theories of tidal
dissipation and irradiated brown dwarf atmospheres.Comment: 30 pages, 19 figures. Submitted to Ap
Type IIb Supernova SN 2011dh: Spectra and Photometry from the Ultraviolet to the Near-Infrared
We report spectroscopic and photometric observations of the Type IIb SN
2011dh obtained between 4 and 34 days after the estimated date of explosion
(May 31.5 UT). The data cover a wide wavelength range from 2,000 Angstroms in
the UV to 2.4 microns in the NIR. Optical spectra provide line profiles and
velocity measurements of HI, HeI, CaII and FeII that trace the composition and
kinematics of the SN. NIR spectra show that helium is present in the atmosphere
as early as 11 days after the explosion. A UV spectrum obtained with the STIS
reveals that the UV flux for SN 2011dh is low compared to other SN IIb. The HI
and HeI velocities in SN 2011dh are separated by about 4,000 km/s at all
phases. We estimate that the H-shell of SN 2011dh is about 8 times less massive
than the shell of SN 1993J and about 3 times more massive than the shell of SN
2008ax. Light curves (LC) for twelve passbands are presented. The maximum
bolometric luminosity of erg s occurred
about 22 days after the explosion. NIR emission provides more than 30% of the
total bolometric flux at the beginning of our observations and increases to
nearly 50% of the total by day 34. The UV produces 16% of the total flux on day
4, 5% on day 9 and 1% on day 34. We compare the bolometric light curves of SN
2011dh, SN 2008ax and SN 1993J. The LC are very different for the first twelve
days after the explosions but all three SN IIb display similar peak
luminosities, times of peak, decline rates and colors after maximum. This
suggests that the progenitors of these SN IIb may have had similar compositions
and masses but they exploded inside hydrogen shells that that have a wide range
of masses. The detailed observations presented here will help evaluate
theoretical models for this supernova and lead to a better understanding of SN
IIb.Comment: 23 pages, 14 figures, 9 tables, accepted by Ap
Discovery and Precise Characterization by the MEarth Project of LP 661-13, an Eclipsing Binary Consisting of Two Fully Convective Low-mass Stars
We report the detection of stellar eclipses in the LP 661-13 system. We
present the discovery and characterization of this system, including high
resolution spectroscopic radial velocities and a photometric solution spanning
two observing seasons. LP 661-13 is a low mass binary system with an orbital
period of days at a distance of parsecs. LP 661-13A is a star while LP
661-13B is a star. The radius of each component
is and ,
respectively. We detect out of eclipse modulations at a period slightly shorter
than the orbital period, implying that at least one of the components is not
rotating synchronously. We find that each component is slightly inflated
compared to stellar models, and that this cannot be reconciled through age or
metallicity effects. As a nearby eclipsing binary system where both components
are near or below the full-convection limit, LP 661-13 will be a valuable test
of models for the structure of cool dwarf stars.Comment: 24 pages, 8 tables, 6 figures. Submitted to ApJ, comments welcom
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