- ID:
- ivo://CDS.VizieR/J/A+A/473/829
- Title:
- Orbital elements of 156 spectroscopic binaries
- Short Name:
- J/A+A/473/829
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a comprehensive, long-term monitoring programme aiming to improve our knowledge of such binary systems. We monitored the radial velocities of 1309 red giants in 187 open clusters with the Coravel spectrometers for 20 years, with a typical accuracy of 0.4km/s per observation. In total, 289 spectroscopic binaries were detected in the sample. We present first orbits for 67 systems and improved elements for another 64 previously published orbits, based on additional observations. For completeness, 25 published orbits are listed as well. The orbits are based on a total of 4039 observations, an average of 26 per system. Orbital periods range from 41.5 to 14722-days (40yrs), eccentricities from 0.00 to 0.81. The remaining systems have too long periods and/or inadequate phase coverage for an orbit determination at this time or too few observations.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/399/2146
- Title:
- Orbits of open clusters in the Galaxy
- Short Name:
- J/MNRAS/399/2146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyse the kinematics and orbits for a sample of 488 open clusters (OCs) in the Galaxy. The velocity ellipsoid for our present sample is derived as ({sigma}(U),{sigma}(V),{sigma}(W)) = (28.7, 15.8, 11.0)km/s which represents a young thin-disc population. We also confirm that the velocity dispersions increase with the age of a cluster subsample. The orbits of OCs are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of b=-0.070+/-0.011dex/kpc. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of b=-0.082+/-0.014dex/kpc. The distribution of derived orbital eccentricities for OCs is very similar to that derived for the field population of dwarfs and giants in the thin disc.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/1793
- Title:
- 25 Ori group low-mass stars
- Short Name:
- J/MNRAS/444/1793
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a survey of the low-mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA (Centro de Investigaciones de Astronomia Francisco J. Duarte, Merida, Venezuela) Deep Survey of Orion, near-IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low-resolution spectroscopy obtained with Hectospec at the MMT telescope, we selected 1246 photometric candidates to low-mass stars and brown dwarfs with estimated masses within 0.02<~M/M_{sun}_<~0.8 and spectroscopically confirmed a sample of 77 low-mass stars as new members of the cluster with a mean age of ~7Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices {alpha}3=-1.73+/-0.31 and {alpha}2=0.68+/-0.41 in the mass ranges 0.03<=M/M_{sun}_<=0.08 and 0.08<=M/M_{sun}_<=0.5, respectively, or a Scalo lognormal function with coefficients m_c_=0.21^+0.02^_-0.02_ and {sigma}=0.36+/-0.03 in the mass range 0.03<=M/M_{sun}_<=0.8. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the east-west elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low-mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low-mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged.
- ID:
- ivo://CDS.VizieR/J/AJ/159/272
- Title:
- Orion Nebula Cluster PMs with HST Treasury Program
- Short Name:
- J/AJ/159/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of high-precision proper motions in the Orion Nebula Cluster (ONC), based on Treasury Program observations with the Hubble Space Telescope's (HST) ACS/WFC camera. Our catalog contains 2454 objects in the magnitude range of 14.2<m_F775W_<24.7, thus probing the stellar masses of the ONC from ~0.4M{sun} down to ~0.02M{sun} over an area of ~550arcmin^2^. We provide a number of internal velocity dispersion estimates for the ONC that indicate a weak dependence on stellar location and mass. There is good agreement with the published velocity dispersion estimates, although nearly all of them (including ours at {sigma }_{v,x}_=0.94 and {sigma}_{v,y}_=1.25mas/yr) might be biased by the overlapping young stellar populations of Orion A. We identified four new ONC candidate runaways based on HST and the Gaia DR 2 data, all with masses less than ~1M{sun}. The total census of known candidate runaway sources is 10-one of the largest samples ever found in any Milky Way open star cluster. Surprisingly, none of them have tangential velocities exceeding 20km/s. If most of them indeed originated in the ONC, it may compel the re-examination of dynamical processes in very young star clusters. It appears that the mass function of the ONC is not significantly affected by the lost runaways.
- ID:
- ivo://CDS.VizieR/J/ApJS/160/511
- Title:
- Orion Nebula Cluster proplyd candidates
- Short Name:
- J/ApJS/160/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the X-ray and near-infrared emission properties of a sample of pre-main-sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for circumstellar disks ("proplyds") and optical jets in Hubble Space Telescope (HST) imaging. Our study uses X-ray data acquired during Chandra Orion Ultradeep Program (COUP) observations, as well as complementary optical and near-infrared data recently acquired with HST and the Very Large Telescope (VLT), respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/299/39
- Title:
- Orion Trapezium area ROSAT PSPC obs. I.
- Short Name:
- J/A+A/299/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep ROSAT PSPC image centred on the Orion Trapezium has revealed that most of the X-ray emission originates from discrete sources, in contrast to previous EINSTEIN data which suggested a diffuse emission component. We present a list of 171 X-ray sources all situated in the so-called inner ring of the field of view (20' radius). The field is crowded with sources. A special procedure had to be developed to cope with the severe blending of sources. The present list is not complete for L_X_<3.5*10^29^erg/s due to this reason and many more sources can still be expected by a next step in the reduction. Nearly all of the sources could be identified with pre-main sequence stars of the Ori OB 1 association in its subgroups Ic and Id. The statistics of this ensemble are discussed. It seems that members of the above subgroups can be distinguished on the basis of an additional amount of X-ray extinction seen in their spectra or hardness ratios. The O stars in the area ({teta}1 Ori C, {teta}2 Ori A and {iota} Ori) are briefly discussed. Six B stars are identified with X-ray sources.
- ID:
- ivo://CDS.VizieR/J/AN/321/81
- Title:
- Orion Trapezium area ROSAT PSPC obs. II.
- Short Name:
- J/AN/321/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep ROSAT PSPC image centred on the Orion Trapezium has been reduced a second time using an improved version of the PSF to fit the data. The outer rim of the field of view was also included. The new catalogue contains 316 X-ray sources which are easily identified with pre-main sequence stars of the Ori OB1 Ic and Id association. All 316 sources were tested for variability. No variations were found inside the single exposures of about 45 minutes length each. Between the 4 exposures spaced over 5 days about 1/3 of the sources show signs of activities of various forms. As above 25% of these have somewhat regular lights curves (monotonically rising or falling or hill- shaped) we infer that at least some outbursts with time scales longer than a day are present and that past searches for X-ray flares of pre-main sequence stars were biased towards shorter time scales.
- ID:
- ivo://CDS.VizieR/J/AJ/117/1375
- Title:
- Orion Trapezium cluster
- Short Name:
- J/AJ/117/1375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have imaged an area ~5arcmin^2^ at the center of the Trapezium cluster in Orion in the K band using the University of Hawaii (UH) adaptive optics system at the UH 2.2 m telescope. Our survey detects 292 stars brighter than K=18.2mag and resolves pairs to the 0.23" diffraction limit of the telescope. The binary fraction in the angular separation range 0.3"-0.6", corresponding to 132-264AU at 440pc, is indistinguishable from that of the solar-like stars in the solar neighborhood. Proplyds are associated with both single stars and visual binaries. About half the stars in our sample have also been measured at V and I by Prosser et al. (1994ApJ...421..517P); most of these seem to be about 10^6^yr old, observed through moderate extinction, and having some excess emission at K. The luminosity function turns over before the stellar limit of ~13.5mag, indicating that the cluster does not contain a large population of massive brown dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/L117
- Title:
- Oxygen in Pleiades and M34 dwarfs
- Short Name:
- J/ApJ/602/L117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the high-excitation O I {lambda}7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation {lambda}6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] {lambda}6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]_6300_=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]_Trip_ at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures.
- ID:
- ivo://CDS.VizieR/J/AJ/142/60
- Title:
- Palomar Transient Factory Orion Project
- Short Name:
- J/AJ/142/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Palomar Transient Factory (PTF) Orion project is one of the experiments within the broader PTF survey, a systematic automated exploration of the sky for optical transients. Taking advantage of the wide (3.5{deg}x2.3{deg}) field of view available using the PTF camera installed at the Palomar 48 inch telescope, 40 nights were dedicated in 2009 December to 2010 January to perform continuous high-cadence differential photometry on a single field containing the young (7-10Myr) 25 Ori association. Little is known empirically about the formation of planets at these young ages, and the primary motivation for the project is to search for planets around young stars in this region. The unique data set also provides for much ancillary science. In this first paper, we describe the survey and the data reduction pipeline, and present some initial results from an inspection of the most clearly varying stars relating to two of the ancillary science objectives: detection of eclipsing binaries and young stellar objects.
