Search results for "Radial velocity"
showing 10 items of 45 documents
Spectroscopic observations of blue stars with infrared excesses in NGC 6611
2013
The young open cluster NGC 6611 includes among its candidate members a class of peculiar objects with interesting properties: blue stars with infrared IR excesses. These stars show excesses in IR bands, signature of the presence of a circumstellar disk, but optical colors typical of older field stars. In order to confirm their membership to the cluster, it is therefore important to use new spectroscopic observations, together with previous photometric data. We aim at confirming the membership of these objects and at investigating their physical properties to verify whether the observed colors are intrinsic or altered by the presence of the disk or by the accretion processes. We analyze the …
FLAMES Observations of the Star Forming Region NGC 6530
2006
Context. Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. Aims. We select cluster members using different membership criteria, to study the properties of pre-main sequence stars with or without circumstellar disks. Methods. We use intermediate resolution spectra including the Li I 6707.8 $\AA$ line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined …
An abundance analysis of the single-lined spectroscopic binaries with barium stars-like orbital elements
1997
Detailed abundance analyses have been car- ried out for 17 single-lined binaries (giants and dwarfs) with orbital elements and mass functions similar to those of barium stars, using high-dispersion CCD spectra and model atmospheres. All these binary systems contain an unseen low-mass component, presumably, a white dwarf. A mild enhancement (+0:1 0:25 dex) of the averaged s- process elements abundances has been found only for two stars. The heavy-element overabundances in these stars are much less marked than those of the classical barium stars having similar orbital periods. We have concluded that the existence of a white dwarf (WD) companion in binary systems with barium star like characte…
Spectroscopic variability of IRAS22272+5435
2015
A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS22272+5435 (HD235858), along with a simultaneous monitoring of its radial velocity and $BVR_C$ magnitudes. The object is known to vary in light, color, and velocity due to pulsation with a period of 132 days. The light and color variations are accompanied by significant changes in spectral features, most of which are identified as lines of carbon-bearing molecules. According to the observations, the $C_2$ Swan system and CN Red system lines are stronger near the light minimum. A photospheric spectrum of the central star was calculated using new self-consistent atm…
Photometric and Hα Observations of LSI+61°303
1994
The Be massive X-ray binary LSI+61°303 is a 26.5 days periodic radiosource (Taylor & Gregory, 1984), exhibiting radio outbursts maxima between phases 0.6-0.8. Evidence of a photometric period of similar value has also been reported (Paredes & Figueras, 1986; Mendelson & Mazeh, 1989). The previous spectroscopic radial velocity observations of Hutchings & Crampton (1981) are in agreement with the radio period, and give support to the presence of a companion. We present new optical and infrared photometric observations and high resolution Hα spectra of LSI+61°303.
A detailed spectroscopy of the carbon-rich star BD +57° 2161
2005
An LTE abundance analysis based on high-resolution spectra is presented for the carbon-rich star BD +57° 2161, whose evolutionary status is unknown. With [C/Fe] = +0.4 dex and a mean s-process overabundance of [s/Fe] ≃ +1.5 dex the peculiar atmospheric composition of BD +57° 2161 is confirmed. The 12 C/ 13 C abundance ratio was found to be about 10. The mild iron deficiency, [Fe/H] = -0.2, supports the idea that BD +57° 2161 could be an old-disk-population object. Radial-velocity measurements confirm the binary nature of the star. Therefore the peculiar chemical composition could be due to the mass transfer from the secondary - AGB star in the past. Orbital parameters are estimated for anot…
NGC1600 - Cluster or Field Elliptical?
2008
A study of the galaxy distribution in the field of the elliptical galaxy NGC1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighbouring galaxies are much fainter and could be taken as satellites of NGC1600. The number density profile of galaxies in the field of this galaxy shows a decline with radius, with evidence of a background at approximately 1.3 Mpc. The density and number density profile are consistent with that found for other isolated early-type galaxies. NGC1600 appears as an extended source in X-rays, and the center of the X-ray emission seems not to coincide with the center of the galaxy. The velocity distribution of neig…
The GAPS Programme with HARPS-N at TNG XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurem…
2017
Context. Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity (RV) variations similar to those induced by a companion. On the other hand any stellar signal is wavelength dependent, while signals due to a companion are achromatic. Aims. Our goal is to determine the origin of the Doppler periodic variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the presence of a substellar companion. Methods. Several methods have been used to exclude the stellar origin of the observed signal including detailed analysis of…
The Evolution of Disk Winds from a Combined Study of Optical and Infrared Forbidden Lines
2020
We analyze high-resolution (dv=<10km/s) optical and infrared spectra covering the [OI] 6300 angstrom and [NeII] 12.81 micron lines from a sample of 31 disks in different evolutionary stages. Following work at optical wavelengths, we use Gaussian profiles to fit the [NeII] lines and classify them into HVC (LVC) if the line centroid is more (less) blueshifted than 30 km/s with respect to the stellar radial velocity. Unlike for the [OI] where a HVC is often accompanied by a LVC, all 17 sources with a [NeII] detection have either a HVC or a LVC. [NeII] HVCs are preferentially detected toward high accretors (Macc > 10$^{-8}$ Msun/yr) while LVCs are found in sources with low Macc, low [OI] …
Multi-Object Spectroscopy of Open Clusters with FLAMES: Preliminary GTO Results
2006
We report on preliminary results of VLT/FLAMES observations of the old open clusters NGC 2506, Mel 66 and Cr 261, obtained as part of our Guaranteed Time on this instrument. We focus in particular on the very old cluster Cr 261, one of the oldest open clusters in the Galaxy. We compare the derived Li abundances with those of other old clusters, and we discuss briefly Li depletion on the main-sequence from the age of the Hyades to ∼8 Gyr. 1 The GTO Program on Open Clusters With the advent of the multi-object spectrograph FLAMES at the VLT [13], the study of open clusters has received a great boost due both to the larger telescope area and to the multiplexing capability offered by the new ins…