2,361 research outputs found
A homogeneous spectroscopic analysis of host stars of transiting planets
The analysis of transiting extra-solar planets provides an enormous amount of
information about the formation and evolution of planetary systems. A precise
knowledge of the host stars is necessary to derive the planetary properties
accurately. The properties of the host stars, especially their chemical
composition, are also of interest in their own right. Information about planet
formation is inferred by, among others, correlations between different
parameters such as the orbital period and the metallicity of the host stars.
The stellar properties studied should be derived as homogeneously as possible.
The present work provides new, uniformly derived parameters for 13 host stars
of transiting planets. Effective temperature, surface gravity, microturbulence
parameter, and iron abundance were derived from spectra of both high
signal-to-noise ratio and high resolution by assuming iron excitation and
ionization equilibria. For some stars, the new parameters differ from previous
determinations, which is indicative of changes in the planetary radii. A
systematic offset in the abundance scale with respect to previous assessments
is found for the TrES and HAT objects. Our abundance measurements are
remarkably robust in terms of the uncertainties in surface gravities. The iron
abundances measured in the present work are supplemented by all previous
determinations using the same analysis technique. The distribution of iron
abundance then agrees well with the known metal-rich distribution of planet
host stars. To facilitate future studies, the spectroscopic results of the
current work are supplemented by the findings for other host stars of
transiting planets, for a total dataset of 50 objects.Comment: accepted for publication in A&A, 7 pages, 6 figure
Independent confirmation and refined parameters of the hot Jupiter XO-5b
We present HATNet observations of XO-5b, confirming its planetary nature
based on evidence beyond that described in the announcement of Burke et al.
(2008), namely, the lack of significant correlation between spectral bisector
variations and orbital phase. In addition, using extensive spectroscopic
measurements spanning multiple seasons, we investigate the relatively large
scatter in the spectral line bisectors. We also examine possible blended
stellar configurations (hierarchical triples, chance alignments) that can mimic
the planet signals, and we are able to show that none are consistent with the
sum of all the data. The analysis of the S activity index shows no significant
stellar activity. Our results for the planet parameters are consistent with
values in Burke et al. (2008), and we refine both the stellar and planetary
parameters using our data. XO-5b orbits a slightly evolved, late G type star
with mass M_s = 0.88 +/- 0.03, radius R_s = 1.08 +/- 0.04, and metallicity
close to solar. The planetary mass and radius are M_p = 1.059 +/- 0.028 M_Jup
and R_p = 1.109 +/- 0.050 R_Jup, respectively, corresponding to a mean density
of 0.96 -0.11 +0.14 g/cm^3. The ephemeris for the orbit is P = 4.187757 +/-
0.000011, E= 2454552.67168 +/- 0.00029 (BJD) with transit duration of 0.1307
+/- 0.0013 d. By measuring four individual transit centers, we found no signs
for transit timing variations. The planet XO-5b is notable for its anomalously
high Safronov number, and has a high surface gravity when compared to other
transiting exoplanets with similar period.Comment: Accepted for publication in ApJ, 8 pages in emulateapj styl
HAT-P-39b--HAT-P-41b: Three Highly Inflated Transiting Hot Jupiters
We report the discovery of three new transiting extrasolar planets orbiting
moderately bright (V=11.1 to 12.4) F stars. The planets have periods of P =
2.6940 d to 4.4572 d, masses of 0.60 M_J to 0.80 M_J, and radii of 1.57 R_J to
1.73 R_J. They orbit stars with masses between 1.40 M_sun and 1.51 M_sun. The
three planets are members of an emerging population of highly inflated Jupiters
with 0.4 M_J 1.5 R_J.Comment: Submitted to AJ. 16 pages, 11 figures, 12 table
Overtone and multi-mode RR Lyrae stars in the globular cluster M3
The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are
studied using a 200-d long, and time-series photometry
obtained in 2012. 70\% of the 52 overtone variables observed show some kind of
multi-periodicity (additional frequency at
frequency ratio, Blazhko effect, double/multi-mode pulsation, period doubling).
A signal at 0.587 frequency ratio to the fundamental-mode frequency is detected
in the double-mode star, V13, which may be identified as the second radial
overtone mode. If this mode-identification is correct, than V13 is the first RR
Lyrae star showing triple-mode pulsation of the first three radial modes.
Either the Blazhko effect or the frequency (or both of these
phenomena) appear in 7 double-mode stars. The
period ratio of RRd stars showing the Blazhko effect are anomalous. A
displacement of the main frequency component at the fundamental-mode with the
value of modulation frequency (or its half) is detected in three Blazhko RRd
stars parallel with the appearance of the overtone-mode pulsation. The
frequency appears in RRc stars that lie at the blue side of the
double-mode region and in RRd stars, raising the suspicion that its occurrence
may be connected to double-mode pulsation. The changes of the Blazhko and
double-mode properties of the stars are also reviewed using the recent and
archive photometric data.Comment: accepted for publication in ApJ Suppl. 26 pages, 25 figure
HATS-1b: The First Transiting Planet Discovered by the HATSouth Survey
We report the discovery of HATS-1b, a transiting extrasolar planet orbiting
the moderately bright V=12.05 G dwarf star GSC 6652-00186, and the first planet
discovered by HATSouth, a global network of autonomous wide-field telescopes.
HATS-1b has a period P~3.4465 d, mass Mp~1.86MJ, and radius Rp~1.30RJ. The host
star has a mass of 0.99Msun, and radius of 1.04Rsun. The discovery light curve
of HATS-1b has near continuous coverage over several multi-day periods,
demonstrating the power of using a global network of telescopes to discover
transiting planets.Comment: Submitted to AJ 10 pages, 5 figures, 6 table
Superflares on Ordinary Solar-Type Stars
Short duration flares are well known to occur on cool main-sequence stars as
well as on many types of `exotic' stars. Ordinary main-sequence stars are
usually pictured as being static on time scales of millions or billions of
years. Our sun has occasional flares involving up to ergs which
produce optical brightenings too small in amplitude to be detected in
disk-integrated brightness. However, we identify nine cases of superflares
involving to ergs on normal solar-type stars. That is,
these stars are on or near the main-sequence, are of spectral class from F8 to
G8, are single (or in very wide binaries), are not rapid rotators, and are not
exceedingly young in age. This class of stars includes many those recently
discovered to have planets as well as our own Sun, and the consequences for any
life on surrounding planets could be profound. For the case of the Sun,
historical records suggest that no superflares have occurred in the last two
millennia.Comment: 16 pages, accepted for publication in Ap
UCAC3 Proper Motion Survey. I. Discovery of New Proper Motion Stars in UCAC3 with 0.40 "/yr > mu >= 0.18 "/yr between Declinations -90 deg and -47 deg
Presented here are 442 new proper motion stellar systems in the southern sky
between declinations -90\degr and -47\degr with 0\farcs40 yr
0\farcs18 yr. These systems constitute a 25.3% increase in
new systems for the same region of the sky covered by previous SuperCOSMOS
RECONS (SCR) searches that used Schmidt plates as the primary source of
discovery. Among the new systems are 25 multiples, plus an additional seven new
common proper motion companions found to previously known primaries. All stars
have been discovered using the third U.S. Naval Observatory (USNO) CCD
Astrograph Catalog (UCAC3). A comparison of the UCAC3 proper motions to those
from the Hipparcos, Tycho-2, Southern Proper Motion (SPM4), and SuperCOSMOS
efforts is presented, and shows that UCAC3 provides similar values and
precision to the first three surveys. The comparison between UCAC3 and
SuperCOSMOS indicates that proper motions in RA are systematically shifted in
the SuperCOSMOS data but are consistent in DEC data, while overall showing a
significantly higher scatter. Distance estimates are derived for stars having
SuperCOSMOS Sky Survey (SSS) , , and plate magnitudes
and Two-Micron All Sky Survey (2MASS) infrared photometry. We find 15 systems
estimated to be within 25 pc, including UPM 1710-5300 our closest new discovery
estimated at 13.5 pc. Such new discoveries suggest that more nearby stars are
yet to be found in these slower proper motion regimes, indicating that more
work is needed to develop a complete map of the solar neighborhood.Comment: 24 pages, 7 figures, 4 tables, accepted to the Astronomical Journal
July 07, 201
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
The Mass-Radius Relationship for Very Low Mass Stars: Four New Discoveries from the HATSouth Survey
We report the discovery of four transiting F-M binary systems with companions
between 0.1-0.2 Msun in mass by the HATSouth survey. These systems have been
characterised via a global analysis of the HATSouth discovery data, combined
with high-resolution radial velocities and accurate transit photometry
observations. We determined the masses and radii of the component stars using a
combination of two methods: isochrone fitting of spectroscopic primary star
parameters, and equating spectroscopic primary star rotation velocity with
spin-orbit synchronisation. These new very low mass companions are HATS550-016B
(0.110 -0.006/+0.005 Msun, 0.147 -0.004/+0.003 Rsun), HATS551-019B (0.17
-0.01/+0.01 Msun, 0.18 -0.01/+0.01 Rsun), HATS551-021B (0.132 -0.005/+0.014
Msun, 0.154 -0.008/+0.006 Rsun), HATS553-001B (0.20 -0.02/+0.01 Msun, 0.22
-0.01/+0.01 Rsun). We examine our sample in the context of the radius anomaly
for fully-convective low mass stars. Combining our sample with the 13 other
well-studied very low mass stars, we find a tentative 5% systematic deviation
between the measured radii and theoretical isochrone models.Comment: 17 pages, 8 figures, accepted for publication in MNRA
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