144 research outputs found
Signatures of rocky planet engulfment in HAT-P-4. Implications for chemical tagging studies
Aims. To explore the possible chemical signature of planet formation in the
binary system HAT-P-4, by studying abundance vs condensation temperature Tc
trends. The star HAT-P-4 hosts a planet detected by transits while its stellar
companion does not have any detected planet. We also study the Lithium content,
which could shed light on the problem of Li depletion in exoplanet host stars.
Conclusions. The exoplanet host star HAT-P-4 is found to be ~0.1 dex more metal
rich than its companion, which is one of the highest differences in metallicity
observed in similar systems. This could have important implications for
chemical tagging studies, disentangling groups of stars with a common origin.
We rule out a possible peculiar composition for each star as lambda Boo, delta
Scuti or a Blue Straggler. The star HAT-P-4 is enhanced in refractory elements
relative to volatile when compared to its stellar companion. Notably, the
Lithium abundance in HAT-P-4 is greater than in its companion by ~0.3 dex,
which is contrary to the model that explains the Lithium depletion by the
presence of planets. We propose a scenario where, at the time of planet
formation, the star HAT-P-4 locked the inner refractory material in
planetesimals and rocky planets, and formed the outer gas giant planet at a
greater distance. The refractories were then accreted onto the star, possibly
due to the migration of the giant planet. This explains the higher metallicity,
the higher Lithium content, and the negative Tc trend detected. A similar
scenario was recently proposed for the solar twin star HIP 68468, which is in
some aspects similar to HAT-P-4. We estimate a mass of at least Mrock ~ 10
Mearth locked in refractory material in order to reproduce the observed Tc
trends and metallicity.Comment: 5 pages, 6 figures, A&A Letters accepte
Measuring the continuum polarization with ESPaDOnS
Our goal is to test the feasibility to obtain accurate measurements of the
continuum polarization from high-resolution spectra using the
spectropolarimetric mode of ESPaDOnS. We used the new pipeline OPERA to reduce
recent and archived ESPaDOnS data. A couple of standard polarization stars and
several science objects were tested for the linear mode. In addition, the
circular mode was tested using several objects from the archive with expected
null polarization. Synthetic broad-band polarization was computed from the
ESPaDOnS continuum polarization spectra and compared with published values
(when available) to quantify the accuracy of the instrument. The continuum
linear polarization measured by ESPaDOnS is consistent with broad-band
polarimetry measurements available in the literature. The accuracy in the
degree of linear polarization is around 0.2-0.3% considering the full sample.
The accuracy in polarization position angle using the most polarized objects is
better than 5deg. Consistent with this, the instrumental polarization computed
for the circular continuum polarization is also between 0.2-0.3%. Our results
suggest that measurements of the continuum polarization using ESPaDOnS are
viable and can be used to study many astrophysical objects.Comment: 15 pages, 13 figures, accepted to Astronomy and Astrophysic
Kepler Observations of Very Low-Mass Stars
Observations of very low-mass stars with Kepler represent an excellent
opportunity to search for planetary transits and to characterize optical
photometric variability at the cool end of the stellar mass distribution. In
this paper, we present low-resolution red optical spectra that allow us to
identify 18 very low-mass stars that have Kepler light curves available in the
public archive. Spectral types of these targets are found to lie in the range
dM4.5--dM8.5, implying spectrophotometric distances from 17 pc to 80 pc. Limits
to the presence of transiting planets are placed from modelling of the Kepler
light curves. We find that the size of the planets detectable by Kepler around
these small stars typically lie in the range 1 to 5 Earth radii within the
habitable regions (P10 days). We identify one candidate transit with a
period of 1.26 days that resembles the signal produced by a planet slightly
smaller than the Moon. However, our pixel by pixel analysis of the Kepler data
shows that the signal most likely arises from a background contaminating
eclipsing binary. For 11 of these objects reliable photometric periods shorter
than 7 days are derived, and are interpreted as rotational modulation of
magnetic cool spots. For 3 objects we find possible photometric periods longer
than 50 days that require confirmation. H emission measurements and
flare rates are used as a proxies for chromospheric activity and transversal
velocities are used as an indicator of dynamical ages. These data allow us to
discuss the relationship between magnetic activity and detectability of
planetary transits around very low-mass stars. We show that Super-Earth planets
with sizes around 2 Earth radii are detectable with Kepler around about two
thirds of the stars in our sample, independently from their level of
chromospheric activity.Comment: Accepted for publication in Astronomy and Astrophysic
The Mass of HD 38529 c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric
observations of the G4 IV star HD 38529 are combined with the results of the
analysis of extensive ground-based radial velocity data to determine the mass
of the outermost of two previously known companions. Our new radial velocities
obtained with the Hobby-Eberly Telescope and velocities from the
Carnegie-California group now span over eleven years. With these data we obtain
improved RV orbital elements for both the inner companion, HD 38529 b and the
outer companion, HD 38529 c. We identify a rotational period of HD 38529
(P_{rot}=31.65 +/- 0.17 d) with FGS photometry. We model the combined
astrometric and RV measurements to obtain the parallax, proper motion,
perturbation period, perturbation inclination, and perturbation size due to HD
38529 c. For HD 38529 c we find P = 2136.1 +/- 0.3 d, perturbation semi-major
axis \alpha =1.05 +/-0.06i_{Jup}) companion at
P~194 days. Additional observations (radial velocities and/or Gaia astrometry)
are required to validate an interpretation of HD 38529 d as a planetary-mass
companion. If confirmed, the resulting HD 38529 planetary system may be an
example of a "Packed Planetary System".Comment: Accepted by The Astronomical Journa
Identification of strong photometric activity in the components of LHS 1070
Activity in low-mass stars is an important ingredient in the evolution of
such objects. Fundamental physical properties such as age, rotation, magnetic
field are correlated with activity. Aims: We show that two components of the
low-mass triple system LHS 1070 exhibit strong flaring activity. We identify
the flaring components and obtained an improved astrometric solution for the
LHS 1070 A/(B+C) system. Methods: Time-series CCD observations were used to
monitor LHS 1070 in the B and I_C bands. H-band data were used to obtain
accurate astrometry for the LHS 1070 A/(B+C) system. Results: We have found
that two components of the triple system LHS 1070 exhibit photometric activity.
We identified that components A and B are the flaring objects. We estimate the
total energy, ~2.0 x 10^{33} ergs, and the magnetic field strength, ~5.5 kG, of
the flare observed in LHS 1070 B. This event is the largest amplitude, \Delta B
> 8.2 mag, ever observed in a flare star.Comment: 5 pages, 5 figures, accepted for publication in A&
The Mass of the Candidate Exoplanet Companion to HD136118 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
We use Hubble Space Telescope Fine Guidance Sensor astrometry and
high-cadence radial velocities for HD136118 from the HET with archival data
from Lick to determine the complete set of orbital parameters for HD136118b. We
find an orbital inclination for the candidate exoplanet of i_{b} = 163.1 +- 3.0
deg. This establishes the actual mass of the object, M_{b} = 42^{+11}_{-18}
MJup, in contrast to the minimum mass determined from the radial velocity data
only, M_{b}sin{i} ~ 12 MJup. Therefore, the low-mass companion to HD 136118 is
now identified as a likely brown dwarf residing in the "brown dwarf desert".Comment: 35 pages, 12 figures, 10 tables. Accepted for publication in
Astrophysical Journa
Espectroscopía Gemini-GRACES de estrellas evolucionadas con enanas marrones
A partir de espectros de alta resolución Gemini-GRACES, aquí se presentan parámetros fundamentales refinados y abundancias químicas detalladas de dos gigantes rojas que albergan enanas marrones, HD 54719 y HD 180314. Las abundancias químicas de ambas estrellas son consistentes con las de aquellas evolucionadas cercanas. HD 180314 presenta una abundancia relativamente alta de litio (A(Li)NLT E = 1.28 dex), que probablemente es remanente de su fase de secuencia principal. El análisis de las metalicidades de ambas estrellas indicaría, como tendencia inicial, que las gigantes con enanas marrones son pobres en metales.Based on high-resolution spectra from Gemini-GRACES, here we present refined fundamental parameters and detailed chemical abundances of two red giants hosting brown dwarfs, HD 54719 and HD 180314. The abundances of both stars are consistent with those of nearby evolved thin disk stars. HD 180314 presents a relatively high abundance of lithium (A(Li)NLT E = 1.28 dex), which is likely a remnant from the main-sequence phase. The metallicities of both stars show, as an initial trend, that giants with brown dwarfs are metal-poor.Fil: Zuloaga, Camila. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Jofré, Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Petrucci, Romina Paola. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Martioli, Eder. Laboratorio Nacional de Astrofisica; Brasi
Modeling Multi-Wavelength Stellar Astrometry. III. Determination of the Absolute Masses of Exoplanets and Their Host Stars
Astrometric measurements of stellar systems are becoming significantly more
precise and common, with many ground and space-based instruments and missions
approaching 1 microarcsecond precision. We examine the multi-wavelength
astrometric orbits of exoplanetary systems via both analytical formulae and
numerical modeling. Exoplanets have a combination of reflected and thermally
emitted light that cause the photocenter of the system to shift increasingly
farther away from the host star with increasing wavelength. We find that, if
observed at long enough wavelengths, the planet can dominate the astrometric
motion of the system, and thus it is possible to directly measure the orbits of
both the planet and star, and thus directly determine the physical masses of
the star and planet, using multi-wavelength astrometry. In general, this
technique works best for, though is certainly not limited to, systems that have
large, high-mass stars and large, low-mass planets, which is a unique parameter
space not covered by other exoplanet characterization techniques. Exoplanets
that happen to transit their host star present unique cases where the physical
radii of the planet and star can be directly determined via astrometry alone.
Planetary albedos and day-night contrast ratios may also be probed via this
technique due to the unique signature they impart on the observed astrometric
orbits. We develop a tool to examine the prospects for near-term detection of
this effect, and give examples of some exoplanets that appear to be good
targets for detection in the K to N infrared observing bands, if the required
precision can be achieved.Comment: Accepted to the Astrophysical Journal. 9 pages, 6 figures, 1 table in
emulateapj forma
- …