207 research outputs found
The young binary HD 102077: Orbit, spectral type, kinematics, and moving group membership
The K-type binary star HD 102077 was proposed as a candidate member of the TW
Hydrae Association (TWA) which is a young (5-15 Myr) moving group in close
proximity (~50 pc) to the solar system. The aim of this work is to verify this
hypothesis by different means. We first combine diffraction-limited
observations from the ESO NTT 3.5m telescope in SDSS-i' and -z' passbands and
ESO 3.6m telescope in H-band with literature data to obtain a new, amended
orbit fit, estimate the spectral types of both components, and reanalyse the
Hipparcos parallax and proper motion taking the orbital motion into account.
Moreover, we use two high-resolution spectra of HD 102077 obtained with the
fibre-fed optical echelle spectrograph FEROS at the MPG/ESO 2.2m telescope to
determine the radial velocity and the lithium equivalent width of the system.
The trajectory of HD 102077 is well constrained and we derive a total system
mass of M and a semi-major axis of AU. From the i'-z' colours we infer an integrated spectral type of K2V,
and individual spectral types of K0 +/- 1 and K5 +/- 1. The radial velocity
corrected for the orbital motion of the system is km/s. Even
though the parallax determination from the Hipparcos data is not influenced by
the orbital motion, the proper motion changes to mas/yr and mas/yr. With
the resultant space motion, the probability of HD 102077 being a member of TWA
is less than 1%. Furthermore, the lithium equivalent width of m\AA
is consistent with an age between 30 Myr and 120 Myr and thus older than
the predicted age of TWA. In conclusion, HD 102077's age, galactic space
motion, and position do not fit TWA or any other young moving group
Search for extrasolar planets around young stars in the presence of stellar activity
Planets form in circumstellar disks around newly born stars. The timescales of planet formation and migration remain poorly constrained and are a matter of ongoing debate.
The disk dispersal timescale, which sets a limit to the duration of planet formation, was derived from infrared surveys to be less than 10Myr. In order to test the predicted planet formation time scales described in current theories, it is important to find planets in the age range of 1 to 100Myrs. In the same manner, non-detections can help to understand the current theories. However, the number of discoveries is still very small due to the challenging task to analyze RV signals contaminated by the high stellar activity.
Within this thesis, I performed a systematic radial velocity (RV) search for planets around 21 young targets with ages between ~3 and ~400Myr and spectral types between F6 and M0. In order to account for the strong stellar activity, I analyzed the stellar spectra in terms of a variety of activity indicators, analyzing both single spectral lines and the RV cross-correlation function. For three targets, a strong radial velocity signal could be identified, which was not induced by measurement sampling. Due to the analysis of available photometric data and activity indicators, it was possible to exhibit stellar activity patterns such as cool stellar spots as origin of the signal. The simulation with a spot program allowed to reconstruct possible spot scenarios that could have caused the detected RV variability.
The challenge of the conformation of a transit planet with follow-up observations in presence of stellar activity is shown in the discussion of HATS-2b, a transiting extrasolar planet orbiting a K-type star showing starspot activity.
Furthermore, the discussion of a possible companion around the young eruptive star EX Lupi is part of this thesis. The detailed RV and activity analyses show the challenging task to disentangle RV signals caused by a possible companions and by stellar activity.
Although no planet could be identified in the RV search around 21 young stars, it can in summary be stated that the detailed analyses in this thesis allow to put constraints on further RV surveys looking for exoplanets around young stars. This includes not only the sample size and target selection but also the observations and data analysis methods
Reanalysis of the FEROS observations of HIP 11952
Aims. We reanalyze FEROS observations of the star HIP 11952 to reassess the
existence of the proposed planetary system. Methods. The radial velocity of the
spectra were measured by cross-correlating the observed spectrum with a
synthetic template. We also analyzed a large dataset of FEROS and HARPS
archival data of the calibrator HD 10700 spanning over more than five years. We
compared the barycentric velocities computed by the FEROS and HARPS pipelines.
Results. The barycentric correction of the FEROS-DRS pipeline was found to be
inaccurate and to introduce an artificial one-year period with a semi-amplitude
of 62 m/s. Thus the reanalysis of the FEROS data does not support the existence
of planets around HIP 11952.Comment: 7 pages, 8 figures, 1 tabl
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
Radial velocity variations in the young eruptive star EX Lupi
Context. EX Lup-type objects (EXors) are low-mass pre-main sequence objects characterized by optical and near-infrared outbursts attributed to highly enhanced accretion from the circumstellar disk onto the star.
Aims: The trigger mechanism of EXor outbursts is still debated. One type of theory requires a close (sub)stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we study the radial velocity (RV) variations of EX Lup, the prototype of the EXor class, and test whether they can be related to a close companion.
Methods: We conducted a five-year RV survey, collecting 54 observations with HARPS and FEROS. We analyzed the activity of EX Lup by checking the bisector, the equivalent width of the Ca 8662 Ă
line, the asymmetry of the Ca II K line, the activity indicator SFEROS, the asymmetry of the cross-correlation function, the line depth ratio of the VI/FeI lines, and the TiO, CaH 2, CaH 3, CaOH, and Halpha indices. We complemented the RV measurements with a 14-day optical/infrared photometric monitoring to look for signatures of activity or varying accretion.
Results: We found that the RV of EX Lup is periodic (P = 7.417 d), with stable period, semi-amplitude (2.2 km s-1), and phase over at least four years of observations. This period is not present in any of the above-mentioned activity indicators. However, the RVs of narrow metallic emission lines suggest the same period, but with an anti-correlating phase. The observed absorption line RVs can be fitted with a Keplerian solution around a 0.6 M&sun; central star with msini = (14.7 ± 0.7) MJup and eccentricity of e = 0.24. Alternatively, we attempted to model the observations with a cold or hot stellar spot as well. We found that in our simple model, the spot parameters needed to reproduce the RV semi-amplitude are in contradiction with the photometric variability, making the spot scenario unlikely.
Conclusions: We qualitatively discuss two possibilities to explain the RV data: a geometry with two accretion columns rotating with the star, and a single accretion flow synchronized with the orbital motion of the hypothetical companion; the second scenario is more consistent with the observed properties of EX Lup. In this scenario, the companion's mass would fall into the brown dwarf desert, which, together with the unusually small separation of 0.06 au would make EX Lup a unique binary system. The companion also has interesting implications on the physical mechanisms responsible for triggering the outburst
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 of P â 3.4465 days, mass of Mp â 1.86 MJ, and radius of Rp â 1.30 RJ. The host star has a mass of 0.99 Mâ and radius of 1.04 Râ. The discovery light curve of HATS-1b has near-continuous coverage over several multi-day timespans, demonstrating the power of using a global network of telescopes to discover transiting planets.Development of the HATSouth project was funded by NSF
MRI grant NSF/AST-0723074, operations are supported by
NASA grant NNX09AB29G, and follow-up observations received
partial support from grant NSF/AST-1108686. Followup
observations with the ESO 2.2 m/FEROS instrument were performed under MPI guaranteed time (P087.A-9014(A),
P088.A-9008(A), P089.A-9008(A)) and Chilean time (P087.C-
0508(A)). A.J. acknowledges support from Fondecyt project
1095213, Ministry of Economy ICM Nuclei P07-021-F and
P10-022-F, Anillo ACT-086 and BASAL CATA PFB-06. V.S.
acknowledges support form BASAL CATA PFB-06. M.R. acknowledges
support from a Fondencyt postdoctoral fellowship
N 3120097 and contributions from the ALMA-CONICYT
FUND Project N 31090015. R.B. and N.E. acknowledge support
from Fondecyt project 1095213. Work at the
Australian National University is supported by ARC Laureate
Fellowship Grant FL0992131. We acknowledge the use of
the AAVSO Photometric All-Sky Survey (APASS), funded by
the Robert Martin Ayers Sciences Fund, and the SIMBAD
database, operated at CDS, Strasbourg, France
HATS-4b: A dense hot Jupiter transiting a super metal-rich G star
We report the discovery by the HATSouth survey of HATS-4b, an extrasolar planet transiting a V = 13.46 mag
G star. HATS-4b has a period of P â 2.5167 days, mass of Mp â 1.32 MJup, radius of Rp â 1.02 RJup, and
density of Ïp = 1.55 ± 0.16 g cmâ3 â 1.24 ÏJup. The host star has a mass of 1.00 M , a radius of 0.92 R , and a
very high metallicity [Fe/H]= 0.43 ± 0.08. HATS-4b is among the densest known planets with masses between
1 and 2 MJ and is thus likely to have a significant content of heavy elements of the order of 75 Mâ. In this paper
we present the data reduction, radial velocity measurements, and stellar classification techniques adopted by the
HATSouth survey for the CORALIE spectrograph. We also detail a technique for simultaneously estimating v sin i
and macroturbulence using high resolution spectra.Development of the HATSouth project was funded by NSFMRI
grant NSF/AST-0723074, operations have been supported by
NASA grants NNX09AB29G and NNX12AH91H, and followup
observations receive partial support from grant NSF/AST-
1108686. A.J. acknowledges support from FONDECYT project
1130857, BASAL CATA PFB-06, and projects IC120009 âMillennium
Institute of Astrophysics (MAS)â and P10-022-F of the
Millennium Science Initiative, Chilean Ministry of Economy.
R.B. and N.E. are supported by CONICYT-PCHA/Doctorado
Nacional. R.B. acknowledges additional support from Nucleus
P10-022-F of the Millennium Science Initiative, Chilean Ministry
of Economy. V.S. acknowledges support form BASAL
CATA PFB-06. M.R. acknowledges support from FONDECYT
postdoctoral fellowship 3120097. Australian access to the Magellan Telescopeswas supported
through the National Collaborative Research Infrastructure
Strategy of the Australian Federal Government. Work at the Australian National University is supported by
ARC Laureate Fellowship Grant FL0992131. We acknowledge
the use of the AAVSO Photometric All-Sky Survey (APASS),
funded by the RobertMartin Ayers Sciences Fund, NASAâs Astrophysics
Data System Bibliographic Services, and the SIMBADdatabase,
operated at CDS, Strasbourg, France. Operations
at the MPG/ESO 2.2 m Telescope are jointly performed by the
Max Planck Gesellschaft and the European Southern Observatory
Hats-3b: An inflated hot jupiter transiting an F-type star
We report the discovery by the HATSouth survey of HATS-3b, a transiting extrasolar planet orbiting a V = 12.4 F dwarf star. HATS-3b has a period of P = 3.5479 days, mass of Mp = 1.07 M J, and radius of R p = 1.38 R J. Given the radius of the planet, the
Synthesis and preliminary DNA-binding studies of diimineplatinum(II) complexes containing 3-or 4-pyridineboronic acid
HATS-2b: A transiting extrasolar planet orbiting a K-type star showing starspot activity
We report the discovery of HATS-2b, the second transiting extrasolar planet
detected by the HATSouth survey. HATS-2b is moving on a circular orbit around a
V=13.6 mag, K-type dwarf star (GSC 6665-00236), at a separation of 0.0230 \pm
0.0003 AU and with a period of 1.3541 days. The planetary parameters have been
robustly determined using a simultaneous fit of the HATSouth,
MPG/ESO~2.2\,m/GROND, Faulkes Telescope South/Spectral transit photometry and
MPG/ESO~2.2\,m/FEROS, Euler~1.2\,m/CORALIE, AAT~3.9\,m/CYCLOPS radial-velocity
measurements. HATS-2b has a mass of 1.37 \pm 0.16 M_J, a radius of 1.14 \pm
0.03 R_J and an equilibrium temperature of 1567 \pm 30 K. The host star has a
mass of 0.88 \pm 0.04 M_Sun, radius of 0.89 \pm 0.02 R_Sun and shows starspot
activity. We characterized the stellar activity by analysing two photometric
follow-up transit light curves taken with the GROND instrument, both obtained
simultaneously in four optical bands (covering the wavelength range of
3860-9520 \AA). The two light curves contain anomalies compatible with
starspots on the photosphere of the parent star along the same transit chord.Comment: 13 pages, 8 figures, accepted by A&
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