114 research outputs found
The Remarkable Be Star HD110432
HD110432 has gained considerable attention because it is a hard, variable
X-ray source similar to gamma Cas. From time-serial echelle data obtained over
two weeks during 2005 January and February, we find several remarkable
characteristics in the star's optical spectrum. The line profiles show rapid
variations on some nights which can be most likely be attributed to irregularly
occurring and short-lived migrating subfeatures. Such features have only been
observed to date in gamma Cas and AB Dor, two stars for which it is believed
magnetic fields force circumstellar clouds to corotate over the stellar
surface. The star's optical spectrum also exhibits a number of mainly FeII and
HeI emission features with profiles typical of an optically thin disk viewed
edge-on. Using spectral synthesis techniques, we find that its temperature is
9800K +/-300K, that its projected area is a remarkably large 100 stellar areas,
and its emitting volume resides at a distance of 1 AU from the star. We also
find that the star's absorption profiles extend to +/-1000 km/s, a fact which
we cannot explain. Otherwise, HD110432 and gamma Cas share similarly peculiar
X-ray and optical characteristics such as high X-ray temperature, erratic X-ray
variability on timescales of a few hours, optical emission lines, and
submigrating features in optical line profiles. Because of these similarities,
we suggest that this star is a new member of a select class of "gamma Cas
analogs."Comment: 31 pages, 9 figures, accepted by ApJ (3/20/06
Rotational modulation of the photospheric and chromospheric activity in the young, single K2-dwarf PW And
High resolution echelle spectra of PW And (HD~1405) have been taken during
eight observing runs from 1999 to 2002. The detailed analysis of the spectra
allow us to determine its spectral type (K2V), mean heliocentric radial
velocity (V_hel = -11.15 km/s) rotational velocity (vsin{i} = 22.6 km/s), and
equivalent width of the lithium line 6707.8 AA (EW(LiI) = 273 mAA). The
kinematic (Galactic Velocity (U, V, W)) confirms its membership of the Local
Association moving group, in agreement with the age (30 to 80 Myrs) inferred
from the color magnitude diagram and the lithium equivalent width. Photospheric
activity (presence of cool spots that disturb the profiles of the photospheric
lines) has been detected as changes in the the bisectors of the cross
correlation function (CCF) resulting of cross-correlate the spectra of PW And
with the spectrum of a non active star of similar spectral type. These
variations of the CCF bisectors are related to the variations in the measured
radial velocities and are modulated with a period similar to the photometric
period of the star. At the same time, chromospheric activity has been analyzed,
using the spectral subtraction technique and simultaneous spectroscopic
observations of the H_alpha, H_beta, NaI D_1 and D_2$, HeI D_3, MgI b triplet,
CaII H&K, and CaII infrared triplet lines. A flare was observed during the last
observing run of 2001, showing an enhancement in the observed chromospheric
lines. A less powerful flare was observed on 2002 August 23. The variations of
the chromospheric activity indicators seem to be related to the photospheric
activity. A correlation between radial velocity, changes in the CCF bisectors
and equivalent width of different chromospheric lines is observed with a
different behaviour between epochs 1999, 2001 and 2002.Comment: Latex file with 20 pages, 21 figures tar'ed gzip'ed. Full postscript
(text, figures and tables) available at
http://www.ucm.es/info/Astrof/users/dmg/pub_dmg.html Accepted for publication
in: Astronomy & Astrophysics (A&A
The magnetic field and confined wind of the O star ~Orionis~C
In this paper we confirm the presence of a globally-ordered, kG-strength
magnetic field in the photosphere of the young O star ~Orionis~C, and
examine the properties of its optical line profile variations. A new series of
high-resolution MuSiCoS Stokes and spectra has been acquired which
samples approximately uniformly the rotational cycle of ~Orionis~C.
Using the Least-Squares Deconvolution (LSD) multiline technique, we have
succeeded in detecting variable Stokes Zeeman signatures associated with
the LSD mean line profile. These signatures have been modeled to determine the
magnetic field geometry. We have furthermore examined the profi le variations
of lines formed in both the wind and photosphere using dynamic spectra. Based
on spectrum synthesis fitting of the LSD profiles, we determine that the polar
strength of the magnetic dipole component is 1150 \la B_{\rm d}\la 1800~G and
that the magnetic obliquity is 27\degr \la \beta \la 68\degr, assuming
i=45\pm 20\degr. The best-fit values for i=45\degr are ~G and \beta = 50\degr \pm 6\degr (1\sigma). Our data
confirm the previous detection of a magnetic field in this star, and
furthermore demonstrate the sinusoidal variability of the longitudinal field
and accurately determine the phases and intensities of the magnetic extrema.
The analysis of ``photospheric'' and ``wind'' line profile variations supports
previous reports of the optical spectroscopic characteristics, and provides
evidence for infall of material within the magnetic equatorial plane
Search for Doubly-Charged Higgs Boson Production at HERA
A search for the single production of doubly-charged Higgs bosons H^{\pm \pm}
in ep collisions is presented. The signal is searched for via the Higgs decays
into a high mass pair of same charge leptons, one of them being an electron.
The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment
at HERA. No evidence for doubly-charged Higgs production is observed and mass
dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs
boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only
decays into an electron and a muon via a coupling of electromagnetic strength
h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the
H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged
Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3,
masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl
GAUDI: a preparatory archive for the COROT mission
The GAUDI database (Ground-based Asteroseismology Uniform Database Interface,
http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT
(COnvection, ROtation and planetary Transits,
http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory
for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its
intention is to make the ground-based observations obtained in the preparation
of the asteroseismology programme available in a simple and efficient way. It
contains spectroscopic and photometric data together with inferred physical
parameters for more than 1500 objects gathered since January 1998 in 6 years of
observational campaigns. In this paper, the main functionalities and
characteristics of the system are described. The observations have been
collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de
Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory
and Sierra Nevada Observatory.Comment: 12 pages, 3 figures (quality degraded). Accepted for publication in
The Astronomical Journa
The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE
The SHINE project is a 500-star survey performed with SPHERE on the VLT for
the purpose of directly detecting new substellar companions and understanding
their formation and early evolution. Here we present an initial statistical
analysis for a subsample of 150 stars that are representative of the full SHINE
sample. Our goal is to constrain the frequency of substellar companions with
masses between 1 and 75 MJup and semimajor axes between 5 and 300 au. We adopt
detection limits as a function of angular separation from the survey data for
all stars converted into mass and projected orbital separation using the
BEX-COND-hot evolutionary tracks and known distance to each system. Based on
the results obtained for each star and on the 13 detections in the sample, we
use a MCMC tool to compare our observations to two different types of models.
The first is a parametric model based on observational constraints, and the
second type are numerical models that combine advanced core accretion and
gravitational instability planet population synthesis. Using the parametric
model, we show that the frequencies of systems with at least one substellar
companion are , , and
for BA, FGK, and M stars, respectively. We also
demonstrate that a planet-like formation pathway probably dominates the mass
range from 1-75 MJup for companions around BA stars, while for M dwarfs, brown
dwarf binaries dominate detections. In contrast, a combination of binary
star-like and planet-like formation is required to best fit the observations
for FGK stars. Using our population model and restricting our sample to FGK
stars, we derive a frequency of , consistent with
predictions from the parametric model. More generally, the frequency values
that we derive are in excellent agreement with values obtained in previous
studies.Comment: 24 pages, 14 figures, 3 tables. Accepted for publication in A&
The SPHERE Infrared Survey for Exoplanets (SHINE): II. Observations, Data Reduction and Analysis, Detection Performances, and Initial Results
Context. In recent decades, direct imaging has confirmed the existence of substellar companions (exoplanets or brown dwarfs) on wide orbits (>10 au) around their host stars. In striving to understand their formation and evolution mechanisms, in 2015 we initiated the SPHERE infrared survey for exoplanets (SHINE), a systematic direct imaging survey of young, nearby stars that is targeted at exploring their demographics. Aims. We aim to detect and characterize the population of giant planets and brown dwarfs beyond the snow line around young, nearby stars. Combined with the survey completeness, our observations offer the opportunity to constrain the statistical properties (occurrence, mass and orbital distributions, dependency on the stellar mass) of these young giant planets. Methods. In this study, we present the observing and data analysis strategy, the ranking process of the detected candidates, and the survey performances for a subsample of 150 stars that are representative of the full SHINE sample. Observations were conducted in a homogeneous way between February 2015 and February 2017 with the dedicated ground-based VLT/SPHERE instrument equipped with the IFS integral field spectrograph and the IRDIS dual-band imager, covering a spectral range between 0.9 and 2.3 μm. We used coronographic, angular, and spectral differential imaging techniques to achieve the best detection performances for this study, down to the planetary mass regime. Results. We processed, in a uniform manner, more than 300 SHINE observations and datasets to assess the survey typical sensitivity as a function of the host star and of the observing conditions. The median detection performance reached 5σ-contrasts of 13 mag at 200 mas and 14.2 mag at 800 mas with the IFS (YJ and YJH bands), and of 11.8 mag at 200 mas, 13.1 mag at 800 mas, and 15.8 mag at 3 as with IRDIS in H band, delivering one of the deepest sensitivity surveys thus far for young, nearby stars. A total of sixteen substellar companions were imaged in this first part of SHINE: seven brown dwarf companions and ten planetary-mass companions.These include two new discoveries, HIP 65426 b and HIP 64892 B, but not the planets around PDS70 that had not been originally selected for the SHINE core sample. A total of 1483 candidates were detected, mainly in the large field of view that characterizes IRDIS. The color-magnitude diagrams, low-resolution spectrum (when available with IFS), and follow-up observations enabled us to identify the nature (background contaminant or comoving companion) of about 86% of our subsample. The remaining cases are often connected to crowded-field follow-up observations that were missing. Finally, even though SHINE was not initially designed for disk searches, we imaged twelve circumstellar disks, including three new detections around the HIP 73145, HIP 86598, and HD 106906 systems. Conclusions. Nowadays, direct imaging provides a unique opportunity to probe the outer part of exoplanetary systems beyond 10 au to explore planetary architectures, as highlighted by the discoveries of: one new exoplanet, one new brown dwarf companion, and three new debris disks during this early phase of SHINE. It also offers the opportunity to explore and revisit the physical and orbital properties of these young, giant planets and brown dwarf companions (relative position, photometry, and low-resolution spectrum in near-infrared, predicted masses, and contrast in order to search for additional companions). Finally, these results highlight the importance of finalizing the SHINE systematic observation of about 500 young, nearby stars for a full exploration of their outer part to explore the demographics of young giant planets beyond 10 au and to identify the most interesting systems for the next generation of high-contrast imagers on very large and extremely large telescopes. © M. Langlois et al. 2021.SPHERE is an instrument designed and built by a consortium consisting of IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, France), LESIA (Paris, France), Laboratoire Lagrange (Nice, France), INAF – Osservatorio di Padova (Italy), Observatoire de Genève (Switzerland), ETH Zürich (Switzerland), NOVA (Netherlands), ONERA (France) and ASTRON (Netherlands) in collaboration with ESO. SPHERE was funded by ESO, with additional contributions from CNRS (France), MPIA (Germany), INAF (Italy), FINES (Switzerland) and NOVA (Netherlands). SPHERE also received funding from the European CommissionSixth and Seventh Framework Programmes as part of the Optical Infrared Coordination Network for Astronomy (OPTICON) under grant number RII3-Ct-2004-001566 for FP6 (2004-2008), grant number 226604 for FP7 (2009-2012) and grant number 312430 for FP7 (2013-2016). This paper is based on observations collected at the European Southern Observatory under ESO programmes 198.C-0209, 097.C-0865, 095.C-0298, 095.C-0309,096.C-0241. This work has made use of the SPHERE Data Centre, jointly operated by OSUG/IPAG (Grenoble), PYTHEAS/LAM/CeSAM (Marseille), OCA/Lagrange (Nice), Observatoire de Paris/LESIA (Paris), and Observatoire de Lyon (OSUL/CRAL). This work is supported by the French National Research Agency in the framework of the Investissements d’Avenir program (ANR-15-IDEX-02), through the funding of the “Origin of Life” project of the Univ. Grenoble-Alpes. This work is jointly supported by the French National Programms (PNP and PNPS) and by the Action Spécifique Haute Résolution Angulaire (ASHRA) of CNRS/INSU co-funded by CNES. We also thank the anonymous referee for her/his careful reading of the manuscript as well as her/his insightful comments and suggestions. AV acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 757561). A.-M.L. acknowledges funding from French National Research Agency (GIPSE project). C.P. acknowledges financial support from Fondecyt (grant 3190691) and financial support from the ICM (Iniciativa Científica Milenio) via the Núcleo Milenio de Formación Planetaria grant, from the Universidad de Valparaíso. T.H. acknowledges support from the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 832428
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