17 research outputs found
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
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
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 ≈ 3.4465 days, mass of Mp ≈ 1.86 MJ, and radius of Rp ≈ 1.30 RJ. The host star has a mass of 0.99 M⊙ and radius of 1.04 R⊙. 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-5b: A transiting hot saturn from the HATsouth survey
We report the discovery of HATS-5b, a transiting hot Saturn orbiting a G-type star, by the HATSouth survey. HATS-5b has a mass of Mp 0.24 MJ, radius of Rp 0.91 R J, and transits its host star with a period of P 4.7634 days. The radius of HATS-5b is consistent with both theoretical and empirical models. The host star has a V-band magnitude of 12.6, mass of 0.94 M ⊙, and radius of 0.87 R. The relatively high scale height of HATS-5b and the bright, photometrically quiet host star make this planet a favorable target for future transmission spectroscopy follow-up observations. We reexamine the correlations in radius, equilibrium temperature, and metallicity of the close-in gas giants and find hot Jupiter-mass planets to exhibit the strongest dependence between radius and equilibrium temperature. We find no significant dependence in radius and metallicity for the close-in gas giant population.Development of the HATSouth project was funded by NSF
MRI grant NSF/AST-0723074, operations are supported by
NASA grant NNX12AH91H, and follow-up observations receive
partial support from grant NSF/AST-1108686. Work at
the Australian National University is supported by ARC Laureate
Fellowship Grant FL0992131. A.J.
acknowledges support from FONDECYT project 1130857,
BASAL CATA PFB-06, and projects IC120009 “Millennium
Institute of Astrophysics (MAS)” and 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
No3120097. R.B. and N.E. acknowledge support from
CONICYT-PCHA/Doctorado Nacional and Fondecyt project
1130857. 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. Operations
at the MPG/ESO 2.2 m telescope are jointly performed
by the Max Planck Gesellschaft and the European Southern
Observatory. Australian access to the Magellan Telescopes was supported
through the National Collaborative Research Infrastructure
Strategy of the Australian Federal Government
Opening a new window to other worlds with spectropolarimetry
A high level of diversity has already been observed among the planets of our
own Solar System. As such, one expects extrasolar planets to present a wide
range of distinctive features, therefore the characterisation of Earth- and
super Earth-like planets is becoming of key importance in scientific research.
The SEARCH (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission
proposal of this paper represents one possible approach to realising these
objectives. The mission goals of SEARCH include the detailed characterisation
of a wide variety of exoplanets, ranging from terrestrial planets to gas
giants. More specifically, SEARCH will determine atmospheric properties such as
cloud coverage, surface pressure and atmospheric composition, and may also be
capable of identifying basic surface features. To resolve a planet with a semi
major axis of down to 1.4AU and 30pc distant SEARCH will have a mirror system
consisting of two segments, with elliptical rim, cut out of a parabolic mirror.
This will yield an effective diameter of 9 meters along one axis. A phase mask
coronagraph along with an integral spectrograph will be used to overcome the
contrast ratio of star to planet light. Such a mission would provide invaluable
data on the diversity present in extrasolar planetary systems and much more
could be learned from the similarities and differences compared to our own
Solar System. This would allow our theories of planetary formation, atmospheric
accretion and evolution to be tested, and our understanding of regions such as
the outer limit of the Habitable Zone to be further improved.Comment: 23 pages, accepted for publication in Experimental Astronom
Trans-ancestry genome-wide association meta-analysis of prostate cancer identifies new susceptibility loci and informs genetic risk prediction.
Prostate cancer is a highly heritable disease with large disparities in incidence rates across ancestry populations. We conducted a multiancestry meta-analysis of prostate cancer genome-wide association studies (107,247 cases and 127,006 controls) and identified 86 new genetic risk variants independently associated with prostate cancer risk, bringing the total to 269 known risk variants. The top genetic risk score (GRS) decile was associated with odds ratios that ranged from 5.06 (95% confidence interval (CI), 4.84-5.29) for men of European ancestry to 3.74 (95% CI, 3.36-4.17) for men of African ancestry. Men of African ancestry were estimated to have a mean GRS that was 2.18-times higher (95% CI, 2.14-2.22), and men of East Asian ancestry 0.73-times lower (95% CI, 0.71-0.76), than men of European ancestry. These findings support the role of germline variation contributing to population differences in prostate cancer risk, with the GRS offering an approach for personalized risk prediction
Behavioural endophenotypes in mice lacking the auxiliary GABAB receptor subunit KCTD16
Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain and is implicated in the pathophysiology of a number of neuropsychiatric disorders. The GABAB receptors are G-protein coupled receptors consisting of principle subunits and auxiliary potassium channel tetramerization domain (KCTD) subunits. The KCTD subunits 8, 12, 12b and 16 are cytosolic proteins that determine the kinetics of the GABAB receptor response. Previously, we demonstrated that Kctd12 null mutant mice (Kctd12(-/-)) exhibit increased auditory fear learning and that Kctd12(+/-) mice show altered circadian activity, as well as increased intrinsic excitability in hippocampal pyramidal neurons. KCTD16 has been demonstrated to influence neuronal excitability by regulating GABAB receptor-mediated gating of postsynaptic ion channels. In the present study we investigated for behavioural endophenotypes in Kctd16(-/-) and Kctd16(+/-) mice. Compared with wild-type (WT) littermates, auditory and contextual fear conditioning were normal in both Kctd16(-/-) and Kctd16(+/-) mice. When fear memory was tested on the following day, Kctd16(-/-) mice exhibited less extinction of auditory fear memory relative to WT and Kctd16(+/-) mice, as well as more contextual fear memory relative to WT and, in particular, Kctd16(+/-) mice. Relative to WT, both Kctd16(+/-) and Kctd16(-/-) mice exhibited normal circadian activity. This study adds to the evidence that auxillary KCTD subunits of GABAB receptors contribute to the regulation of behaviours that could constitute endophenotypes for hyper-reactivity to aversive stimuli in neuropsychiatric disorders