96 research outputs found
Studies of multiple stellar systems - III. Modulation of orbital elements in the triple-lined system HD 109648
The triple-lined spectroscopic triple system HD 109648 has one of the
shortest periods known for the outer orbit in a late-type triple, 120.5 days,
and the ratio between the periods of the outer and inner orbits is small, 22:1.
With such extreme values, this system should show orbital element variations
over a timescale of about a decade. We have monitored the radial velocities of
HD 109648 with the CfA Digital Speedometers for eight years, and have found
evidence for modulation of some orbital elements. While we see no definite
evidence for modulation of the inner binary eccentricity, we clearly observe
variations in the inner and outer longitudes of periastron, as well as in the
radial velocity amplitudes of the three components. The observational results,
combined with numerical simulations, allow us to put constraints on the
orientation of the orbits.Comment: 11 pages, 7 figures, accepted by MNRA
A variable star survey of the open cluster M37
A CCD photometric study of the dense galactic open cluster M37 is presented
and discussed. The majority of the analysed data are time-series measurements
obtained through an R_C filter. The observations were carried out on seven
nights between December 1999 and February 2000, and have led to the discovery
of 7 new variable stars in the field. Three of them have been unambiguously
identified as W UMa-type eclipsing binaries, while two more are monoperiodic
pulsating stars, most probably high-amplitude delta Scuti-type variables. The
remaining two stars seem to be long-period eclipsing binaries without firm
period determination. Johnson B and V frames have been used to construct a new
colour-magnitude (CM) diagram of the cluster, and to find the locations of the
new variable stars. The pulsating variables are most likely background objects.
The CM diagram is fitted with recent isochrones yielding the main parameters of
the cluster.Comment: 7 pages, 6 figures, accepted for publication in A&
Determinants of bird conservation action implementation and associated population trends of threatened species
Disk or Halo white dwarfs? Kinematic analysis of high proper motion surveys
We present an alternative method for the kinematic analysis of high proper
motion surveys and discuss its application to the survey of Oppenheimer et al.
(2001) for the selection of reliable halo white dwarfs (WDs). The local WD
space density we estimate is (1-2) 10^{-5}MSun/pc^{3}, which is about an order
of magnitude smaller than the value derived in Oppenheimer et al. (2001), and
is consistent with the values obtained from recent reanalyses of the same data
(e.g. Reid et al. 2001, Reyle et al. 2001, Torres et al. 2002, Salim et al.
2004). Our result, which corresponds to a fraction of 0.1%-0.2% of the local
dark matter, does not support the scenario suggested by the microlensing
experiments that ancient cool WDs could contribute significantly to the dark
halo of the Milky Way.Comment: 9 pages, 4 figures, accepted in Astronomy & Astrophysic
Hipparcos red stars in the HpV_{T2} and VI_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibrated
instantaneous (epoch) Cousins color indices using newly derived
photometry. Three new sets of ground-based Cousins data have
been obtained for more than 170 carbon and red M giants. These datasets in
combination with the published sources of photometry served to obtain the
calibration curves linking Hipparcos/Tycho with the Cousins
index. In total, 321 carbon stars and 4464 M- and S-type stars have new
indices. The standard error of the mean is about 0.1 mag or better down
to although it deteriorates rapidly at fainter magnitudes. These
indices can be used to verify the published Hipparcos color
indices. Thus, we have identified a handful of new cases where, instead of the
real target, a random field star has been observed. A considerable fraction of
the DMSA/C and DMSA/V solutions for red stars appear not to be warranted. Most
likely such spurious solutions may originate from usage of a heavily biased
color in the astrometric processing.Comment: 10 figures, 1 electronic table, accepted in A&
Photometry and membership for low mass stars in the young open cluster NGC 2516
We present the results of a 0.86 square degree CCD photometric survey of the
open cluster NGC 2516, which has an age of about 150 Myr and may have a much
lower metallicity than the similarly-aged Pleiades. We select a preliminary
catalogue of 1254 low mass (between 0.2 and 2.0M_{sun}) cluster candidates, of
which about 70--80 percent are expected to be genuine. The mass function is
metallicity dependent, but consistent with a Salpeter-like law (dN/dlog M ~
M^{-alpha}, alpha=+1.47+/-0.11 or alpha=+1.67+/-0.11 for solar and half-solar
metallicities) between 0.7 and 3.0M_{sun}. At lower masses (between 0.3 and
0.7M_{sun}) there is a sharp fall in the mass function, with alpha=-0.75+/-0.20
(solar metallicity) or alpha=-0.49+/-0.13 (half-solar metallicity), which seems
inconsistent with the much flatter mass functions seen in the Pleiades and
field populations. We explain this by demonstrating that mass segregation has
been at work in NGC 2516 -- more than half the cluster low mass stars are
expected to lie outside out survey. The mass of NGC 2516 stars with mass
greater than 0.3M_{sun} inside our survey is 950-1200M_{sun}, depending on
metallicity and what corrections are applied for unresolved binarity.
Correcting for mass segregation increases this to ~1240-1560M_{sun}, about
twice the total mass of the Pleiades.Comment: 27 pages, accepted for Astronomy & Astrophysic
The old Galactic open clusters FSR1716 and Czernik23
Open clusters older than Gyr are rare in the Galaxy. Affected by a
series of mass-decreasing processes, the stellar content of most open clusters
dissolves into the field in a time-scale shorter than Gyr. In this
sense, improving the statistics of old objects may provide constraints for a
better understanding of the dynamical dissolution of open clusters. Isochrone
fits indicate that FSR 1716 is more probably an old ( Gyr) and absorbed
(\aV=6.3\pm0.2) open cluster, located kpc inside the Solar
circle in a contaminated central field. However, we cannot rule out the
possibility of a low-mass, loose globular cluster. Czernik 23 is shown to be an
almost absorption-free open cluster, Gyr old, located about 2.5 kpc
towards the anti-centre. In both cases, Solar and sub-Solar ()
metallicity isochrones represent equally well the stellar sequences. Both star
clusters have a low mass content (\la200 \ms) presently stored in stars.
Their relatively small core and cluster radii are comparable to those of other
open clusters of similar age. These structural parameters are probably
consequence of the several Gyrs of mass loss due to stellar evolution, tidal
interactions with the disk (and bulge in the case of FSR 1716), and possibly
giant molecular clouds. Czernik 23, and especially FSR 1716, are rare examples
of extreme dynamical survivors. The identification of both as such represents
an increase of to the known population of open clusters older than
Gyr in the Galaxy.Comment: 15 pages and 13 figures. Accepted by A&
Old open clusters in the inner Galaxy: FSR1744, FSR89 and FSR31
We establish the nature and derive fundamental and structural parameters of
the recently catalogued objects FSR1744, FSR89 and FSR31. This work intends to
provide clues to constrain the Galactic tidal disruption efficiency, improve
statistics of the open cluster parameter space, and better define their
age-distribution function inside the Solar circle. Properties of the objects
are investigated by means of 2MASS colour-magnitude diagrams and stellar radial
density profiles built with field star decontaminated photometry.
Diagnostic-diagrams for structural parameters are used to help disentangle
dynamical from high-background effects affecting such centrally projected open
clusters. FSR1744, FSR89 and FSR31 are Gyr-class OCs located at Galactocentric
distances 4.0 - 5.6kpc. Compared to nearby OCs, they have small core and
limiting radii. With respect to the small number of OCs observed in the inner
Galaxy, the emerging scenario in the near-infrared favours disruption driven by
dynamical evolution rather than observational limitations associated with
absorption and/or high background levels. Internally, the main processes
associated with the dynamical evolution are, e.g. mass loss by stellar
evolution, mass segregation and evaporation. Externally they are, e.g. tidal
stress from the disk and bulge, and interactions with giant molecular clouds.
FSR1744, FSR89 and FSR31 have structural parameters consistent with their
Galactocentric distances, in the sense that tidally induced effects may have
accelerated the dynamical evolution.Comment: 12 pages and 13 figs; A&A, accepted, July 9, 200
Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for new M dwarfs in
the solar neighbourhood and M giants with high tangential velocities. Methods:
From an all-sky cross-match between the optical Tycho-2 and the near-infrared
2MASS catalogues, we selected objects with proper motions >50mas/yr and very
red V-Ks colours. For the most interesting targets, we collected
multi-wavelength photometry, constructed spectral energy distributions,
estimated effective temperatures and surface gravities from fits to atmospheric
models, performed time-series analysis of ASAS V-band light curves, and
assigned spectral types from low-resolution spectroscopy obtained with CAFOS at
the 2.2m Calar Alto telescope. Results: We got a sample of 59 bright red high
proper-motion objects, including fifty red giants, four red dwarfs, and five
objects reported in this work for the first time. The five new stars have
magnitudes V~10.8-11.3mag, reduced proper motions midway between known dwarfs
and giants, near-infrared colours typical of giants, and effective temperatures
Teff~2900-3400K. From our time-series analysis, we discovered a long secondary
period in Ruber 4 and an extremely long primary period in Ruber 6. With the
CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of
which seems to be one of the brightest metal-poor M giants ever identified.Comment: Accepted in Astronomy & Astrophysic
- …