448 research outputs found
Kinematic parameters and membership probabilities of open clusters in the Bordeaux PM2000 catalogue
We derive lists of proper-motions and kinematic membership probabilities for
49 open clusters and possible open clusters in the zone of the Bordeaux PM2000
proper motion catalogue (). We test
different parametrisations of the proper motion and position distribution
functions and select the most successful one. In the light of those results, we
analyse some objects individually. The segregation between cluster and field
member stars, and the assignment of membership probabilities, is accomplished
by applying a new and fully automated method based on both parametrisations of
the proper motion and position distribution functions, and genetic algorithm
optimization heuristics associated with a derivative-based hill climbing
algorithm for the likelihood optimization. We present a catalogue comprising
kinematic parameters and associated membership probability lists for 49 open
clusters and possible open clusters in the Bordeaux PM2000 catalogue region. We
note that this is the first determination of proper motions for five open
clusters. We confirm the non-existence of two kinematic populations in the
region of 15 previously suspected non-existent objects.Comment: 14 pages, 6 figures, 4 tables. Accepted for publication in Astronomy
& Astrophysic
Finding new sub-stellar co-moving companion candidates - the case of CT Cha
We have searched for close and faint companions around T Tauri stars in the
Chamaeleon star forming region. Two epochs of direct imaging data were taken
with the VLT Adaptive Optics instrument NaCo in February 2006 and March 2007 in
Ks band for the classical T Tauri star CT Cha together with a Hipparcos binary
for astrometric calibration. Moreover a J band image was taken in March 2007 to
get color information. We found CT Cha to have a very faint companion (Ks{0} =
14.6 mag) of ~ 2.67" separation corresponding to ~ 440 AU. We show that CT Cha
A and the faint object form a common proper motion pair and that the companion
is not a non-moving background object (with 4 sigma significance).Comment: 5 pages, 2 figures, Proceedings of the IAU Symposium 249: Exoplanets:
Detection, Formation and Dynamics, Suzhou - China, 22-26 October 200
SSPMJ1102-3431 brown dwarf characterization from accurate proper motion and trigonometric parallax
In 2005, Scholz and collaborators (Scholz et al. 2005) discovered, in a
proper motion survey, a young brown dwarf SSSPMJ1102-3431(SSSPMJ1102) of
spectral type M8.5, probable member of the TW Hydrae Association (TWA) and
possible companion of the T Tauri star TW Hya. The physical characterization of
SSSPMJ1102 was based on the hypothesis that it forms a binary system with TW
Hya. The recent discovery of a probable giant planet inside the TW Hya
protoplanetary disk with a very short-period (Setiawan et al. 2008) and a disk
around SSSPMJ1102 (Riaz and Gizis 2008) make it especially interesting and
important to measure well the physical parameters of SSSPMJ1102. Trigonometric
parallax and proper motion measurements of SSSPMJ1102 are necessary to test for
TWA membership and, thus, to determine the mass and age of this young brown
dwarf and the possibility that it forms a wide binary system with TW Hya. Two
years of regular observations at the ESO NTT/SUSI2 telescope, have enabled us
to determine the trigonometric parallax and proper motion of SSSPMJ1102. Our
parallax and proper motion determination allow us to precisely describe the
physical properties of this low mass object and to confirm its TWA membership.
Our results are not incompatible with the hypothesis that SSSPMJ1102 is a
binary companion of the star TW Hya.Comment: accepted for publication in A&
On the Nature of the Purported Common Proper Motion Companions to the Exoplanet Host Star 51 Peg
Greaves (2006) proposed that three red, high proper motion stars within 10
degrees of 51 Peg (NLTT 54007, 54064, & 55547) are co-moving companions to this
famous exoplanet host star. While the stars clearly have proper motions similar
to 51 Peg, the inferred kinematic parallaxes for these stars produce extremely
inconsistent color-magnitude positions 2 to 4 magnitudes below the main
sequence. All three stars are likely to be background stars unrelated to 51
Peg.Comment: 5 pages, 1 figure, AN, in pres
Orbital motion of the young brown dwarf companion TWA 5 B
With more adaptive optics images available, we aim at detecting orbital
motion for the first time in the system TWA 5 A+B. We measured separation and
position angle between TWA 5 A and B in each high-resolution image available
and followed their change in time, because B should orbit around A. The
astrometric measurement precision is about one milli arc sec. With ten year
difference in epoch, we can clearly detect orbital motion of B around A, a
decrease in separation by ~ 0.0054 arc sec per year and a decrease in position
angle by ~ 0.26 degrees per year. TWA 5 B is a brown dwarf with ~ 25 Jupiter
masses (Neuh\"auser et al. 2000), but having large error bars (4 to 145 Jupiter
masses, Neuh\"auser et al. 2009). Given its large projected separation from the
primary star, ~ 86 AU, and its young age ~ 10 Myrs), it has probably formed
star-like, and would then be a brown dwarf companion. Given the relatively
large changes in separation and position angle between TWA 5 A and B, we can
conclude that they orbit around each other on an eccentric orbit. Some evidence
is found for a curvature in the orbital motion of B around A - most consistent
with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are
detected and show a small-amplitude (~ 18 mas) periodic sinusoid with ~ 5.7 yr
period, i.e., fully consistent with the orbit of the inner close pair TWA 5
Aa+b. Measuring these residuals caused by the photocenter wobble - even in
unresolved images - can yield the total mass of the inner pair, so can test
theoretical pre-main sequence models.Comment: 6 pages, 4 figures, accepted for publication in A&A; corrected typo
in amplitude below Fig.
Direct imaging of extra-solar planets in star forming regions: Lessons learned from a false positive around IM Lup
Most exoplanet imagers consist of ground-based adaptive optics coronagraphic
cameras which are currently limited in contrast, sensitivity and astrometric
precision, but advantageously observe in the near-IR (1- 5{\mu}m). Because of
these practical limitations, our current observational aim at detecting and
characterizing planets puts heavy constraints on target selection, observing
strategies, data reduction, and follow-up. Most surveys so far have thus
targeted young systems (1-100Myr) to catch the putative remnant thermal
radiation of giant planets, which peaks in the near-IR. They also favor systems
in the solar neighborhood (d<80pc), which eases angular resolution requirements
but also ensures a good knowledge of the distance and proper motion, which are
critical to secure the planet status, and enable subsequent characterization.
Because of their youth, it is very tempting to target the nearby star forming
regions, which are typically twice as far as the bulk of objects usually combed
for planets by direct imaging. Probing these interesting reservoirs sets
additional constraints that we review in this paper by presenting the planet
search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup
(Lupus star forming region, 140-190pc). We show and discuss why age
determination, the choice of evolutionary model for the central star and the
planet, precise knowledge of the host star proper motion, relative or absolute
astrometric accuracy, and patience are the key ingredients for exoplanet
searches around more distant young stars. Unfortunately, most of the time,
precision and perseverance are not paying off: we discovered a candidate
companion around IM Lup in 2008, which we report here to be an unbound
background object. We nevertheless review in details the lessons learned from
our endeavor, and additionally present the best detection limits ever
calculated for IM Lup.Comment: 8 pages, 3 figures, 3 tables, accepted to A&
Kinematics of the Young Stellar Objects associated with the Cometary Globules in the Gum Nebula
An analysis of proper motion measurements of the Young Stellar Objects (YSOs)
associated with the Cometary Globules (CGs) in the Gum Nebula is presented.
While earlier studies based on the radial velocity measurements of the CGs
suggested expansion of the system of the CGs, the observed proper motion of the
YSOs shows no evidence for expansion. In particular the kinematics of two YSOs
embedded in CGs is inconsistent with the supernova explosion of the companion
of Pup about 1.5 Myr ago as the cause of the expansion of the CG
system. YSOs associated with the CGs share the average proper motion of the
member stars of the Vela OB2 association. A few YSOs that have relatively large
proper motions are found to show relatively low infrared excesses.Comment: 19 pages, 6 figures, 4 tables, Accepted for publication in MNRA
M2000 : an astrometric catalog in the Bordeaux Carte du Ciel zone +11 degrees < {delta} < +18 degrees
During four years, systematic observations have been conducted in drift scan
mode with the Bordeaux automated meridian circle in the declination band [+11 ;
+18]. The resulting astrometric catalog includes about 2 300 000 stars down to
the magnitude limit V_M=16.3. Nearly all stars (96%) have been observed at
least 6 times, the catalog being complete down to V_M=15.4. The median internal
standard error in position is about 35 mas in the V_M magnitude range [11 ;
15], which degrades to about 50 mas when the faintest stars are considered.
M2000 provides also one band photometry with a median internal standard error
of 0.04 mag. Comparisons with the Hipparcos and bright part of Tycho-2 catalogs
have enabled to estimate external errors in position to be lower than 40 mas.
In this zone and at epoch 1998, the faint part of Tycho-2 is found to have an
accuracy of 116 mas in alpha instead of 82 mas deduced from the model-based
standard errors given in the catalog.Comment: The catalogue can be fetched directly from:
ftp://cdsarc.u-strasbg.fr/cats/I/272 or queried from:
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/272 More information at :
http://www.observ.u-bordeaux.fr/~soubiran/m2000.ht
Large Amplitude Photometric Variability of the Candidate Protoplanet TMR-1C
In their HST/NICMOS observations, Terebey et al. 1998 detected a candidate
protoplanet, TMR-1C, that lies at a separation of about 10" (~1000 AU) from the
Class I protobinary TMR-1 (IRAS 04361+2547). A narrow filament-like structure
was observed extending south-east from the central proto-binary system towards
TMR-1C, suggesting a morphology in which the candidate protoplanet may have
been ejected from the TMR-1 system. Follow-up low-resolution spectroscopy could
not confirm if this object is a protoplanet or a low-luminosity background
star. We present two epochs of near-infrared photometric observations obtained
at the CFHT of TMR-1C. The time span of ~7 years between the two sets of
observations provides with an opportunity to, (a) check for any photometric
variability similar to that observed among young stellar objects, which would
indicate the youth of this source, and, (b) determine the proper motion. TMR-1C
displays large photometric variability between 1 and 2 mag in both the H- and
Ks-bands. From our 2002 observations, we find a (H-Ks) color of 0.3 mag, which
is much bluer than the value of 1.3 mag reported by T98 from HST observations.
Also, we observe brightening in both the H- and Ks-bands when the colors are
bluer, i.e. the object gets redder as it becomes fainter. We have explored the
possible origins for the observed variability, and find extinction due to the
presence of circumstellar material to be the most likely scenario. The observed
large-amplitude photometric variations, and the possible presence of a
circumstellar disk, are strong arguments against this object being an old
background star.Comment: Accepted in A&
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