- ID:
- ivo://CDS.VizieR/J/A+A/416/125
- Title:
- RI photometry in alpha Per and Pleiades
- Short Name:
- J/A+A/416/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photographic astrometry (proper motions and accurate positions), photometry (in the photographic R and I passbands) and membership probabilities for high probability proper motion members of the clusters Alpha Persei and The Pleiades are presented, along with cross-identifications with names from previously known members in the compilation of Prosser & Stauffer (The Stauffer & Prosser Open Cluster Catalogue, priv.comm.) and their corresponding proper motion membership probabilities according to our study. The SuperCOSMOS facility at the Royal Observatory Edinburgh has (using plates from the United Kingdom Schmidt Telescope) produced complete southern sky surveys in BJ, R and I with an additional second epoch R survey. These surveys are now publicly available (Hambly et al. 2001MNRAS.326.1279H). The scanning program has now moved on to the northern hemisphere, using film and glass copies of plates taken by the Oschin Schmidt Telescope on Mount Palomar, California. These data will soon be publicly available.
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- ID:
- ivo://CDS.VizieR/J/A+A/602/A56
- Title:
- R136 JKs photometry from VLT/SPHERE EAO
- Short Name:
- J/A+A/602/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the sharpest near-IR images of the massive cluster R 136 to date, based on the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode. The crowded stellar population in the core of the R 136 starburst compact cluster remains still to be characterized in terms of individual luminosities, age, mass and multiplicity. SPHERE/VLT and its high contrast imaging possibilities open new windows to make progress on these questions. Stacking-up a few hundreds of short exposures in J and Ks spectral bands over a Field of View (FoV) of 10.9"x12.3" centered on the R136a1 stellar component, enabled us to carry a refined photometric analysis of the core of R136. We detected 1110 and 1059 sources in J and Ks images respectively with 818 common sources. Thanks to better angular resolution and dynamic range for 818 common sources being detected, we found that more than 62.6% (16.5%) of the stars, detected both in J and Ks data, have neighbours closer than 0.2" (0.1"). The closest stars are resolved down to the full width at half maximum (FWHM) of the point spread function (PSF) measured by Starfinder. Among newly resolved and/or detected sources R136a1 and R136c are found to have optical companions and R136a3 is resolved as two stars (PSF fitting) separated by 59+/-2mas. This new companion of R136a3 presents a correlation coefficient of 86% in J and 75% in Ks. The new set of detected sources were used to re-assess the age and extinction of R 136 based on 54 spectroscopically stars that have been recently studied with HST slit-spectroscopy (Crowther et al., 2016MNRAS.458..624C) of the core of this cluster. Over 90% of these 54 sources identified visual companions (closer than 0.2"). We found the most probable age and extinction for these sources are 1.8+1.2-0.8Myr, A_J_=(0.45+/-0.5)mag and A_K_=(0.2+/-0.5) mag within the photometric and spectroscopic error-bars. Additionally, using PARSEC evolutionary isochrones and tracks, we estimated the stellar mass range for each detected source (common in J and K data) and plotted the generalized histogram of mass (MF with error-bars). Using SPHERE data, we have gone one step further and partially resolved and studied the IMF covering mass range of (3-300)M_{sun}_ at the age of 1 and 1.5Myr. The density in the core of R 136 (0.1-1.4pc) is estimated and extrapolated in 3D and larger radii (up to 6pc). We show that the stars in the core are still unresolved due to crowding, and the results we obtained are upper limits. Higher angular resolution is mandatory to overcome these difficulties.
- ID:
- ivo://CDS.VizieR/J/A+A/509/A17
- Title:
- R light curves of NGC 6253 variables
- Short Name:
- J/A+A/509/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents the first high-precision variability survey in the field of the intermediate-age, metal-rich open cluster NGC 6253. We discovered 595 variables and we also characterized most of them providing their variability classes, periods and amplitudes. The sample is complete at short periods: we classified 20 pulsating variables, 225 contact systems, 99 eclipsing systems (22 Beta Lyr type, 59 Beta Per type, 18 RS CVn type), and 77 rotational variables. The time-baseline hampered the precise characterization of 173 variables with periods longer than 4-5days. Moreover, we found a cataclysmic system undergoing an outburst of about 2.5mag.
- ID:
- ivo://CDS.VizieR/J/AJ/155/51
- Title:
- Robo-AO binary star systems in 3 open clusters
- Short Name:
- J/AJ/155/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify and roughly characterize 66 candidate binary star systems in the Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive optics imaging data obtained using Robo-AO at the Palomar 60" telescope. Only ~10% of our imaged pairs were previously known. We detect companions at red optical wavelengths, with physical separations ranging from a few tens to a few thousands of au. A three-sigma contrast curve generated for each final image provides upper limits to the brightness ratios for any undetected putative companions. The observations are sensitive to companions with a maximum contrast of ~6^m^ at larger separations. At smaller separations, the mean (best) raw contrast at 2" is 3.8^m^ (6^m^), at 1" is 3.0^m^ (4.5^m^), and at 0.5" is 1.9^m^ (3^m^). Point-spread function subtraction can recover nearly the full contrast in the closer separations. For detected candidate binary pairs, we report separations, position angles, and relative magnitudes. Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are then used to determine the corresponding binary mass ratios, which range from 0.2 to 0.9 in q=m_2_/m_1_. For our sample of roughly solar-mass (FGK type) stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the Pleiades and Praesepe, the overall binary frequency is measured at ~15.5%+/-2%. However, this value should be considered a lower limit to the true binary fraction within the specified separation and mass ratio ranges in these clusters, given that complex and uncertain corrections for sensitivity and completeness have not been applied.
- ID:
- ivo://CDS.VizieR/J/A+A/341/751
- Title:
- ROSAT HRI observations of the Pleiades
- Short Name:
- J/A+A/341/751
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT High Resolution Imager to explore a region of the cluster formerly surveyed with the PSPC. These new observations substantially improve upon both the sensitivity and the spatial resolution for this region of the Pleiades, allowing us to detect 18 cluster members not detected before and 16 members not included in the catalogs used in previous surveys. The high sensitivity of the present observations permits us to obtain more stringent upper limits for 72 additional members and also provides sufficient numbers of stars to enable us to explore the dependence of L_x_ on stellar rotation for the slow rotators of the Pleiades. Using the new high sensitivity X-ray observations and the recent rotational measurements we discuss the activity-rotation relationship in the Pleiades solar type stars. We also present new photometric observations of optical counterparts of a number of X-ray sources detected in previous surveys but not yet identified.
- ID:
- ivo://CDS.VizieR/J/ApJS/102/75
- Title:
- ROSAT Observations of the Pleiades
- Short Name:
- J/ApJS/102/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Of 214 stars in the core of the Pleiades, 99 were detected in X-rays with the ROSAT PSPC. This catalog lists the characteristics of the stars taken from the literature, in table1.dat and the rotational and X-ray characteristics in table5.dat.
- ID:
- ivo://CDS.VizieR/J/A+A/298/115
- Title:
- ROSAT study of Praesepe
- Short Name:
- J/A+A/298/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the ROSAT PSC observations of the Praesepe cluster. 68 Praesepe candidates have been detected, above a threshold of ~2x10^+28^erg/s (2x10^21^W), in the ~4degx4deg area of the cluster covered by the observations. 56 out of the 68 detected objects are cataloged as high probability Praesepe members.
- ID:
- ivo://CDS.VizieR/J/ApJS/91/625
- Title:
- ROSAT survey of the Pleiades
- Short Name:
- J/ApJS/91/625
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained deep ROSAT images of three regions within the Pleiades open cluster. We have detected 317 X-ray sources in these ROSAT PSPC images, 171 of which we associate with certain or probable members of the Pleiades cluster. We detect nearly all Pleiades members with spectral types later than G0 and within 25 arcminutes of our three field centers where our sensitivity is highest. This has allowed us to derive for the first time the luminosity function for the G, K, and M dwarfs of an open cluster without the need to use statistical techniques to account for the presence of upper limits in the data sample. Because of our high X-ray detection frequency down to the faint limit of the optical catalog, we suspect that some of our unidentified X-ray sources are previously unknown, very low-mass members of the Pleiades.
- ID:
- ivo://CDS.VizieR/J/AJ/110/1229
- Title:
- ROSAT X-ray survey in NGC 6475
- Short Name:
- J/AJ/110/1229
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A ROSAT X-ray survey, with complementary optical photometry, of the open cluster NGC 6475 has enabled the detection of ~50 late-F to K0 and ~70 K/M dwarf new candidate members, providing the first reliable detection of low-mass stars in this low galactic latitude, 220Myr old cluster. The X-ray observations reported here have a typical limiting sensitivity of L_X_ ~ 10^29^erg/s. The detection frequency of early type cluster members is consistent with the hypothesis that the X-ray emitting early type stars are binary systems with an unseen, low-mass secondary producing the X-rays. The ratio between X-ray and bolometric luminosity among NGC 6475 members saturates at a spectral-type/color which is intermediate between that in much younger and in much older clusters, consistent with rotational spindown of solar-type stars upon their arrival on the ZAMS. The upper envelope of X-ray luminosity as a function of spectral type is comparable to that of the Pleiades, with the observed spread in X-ray luminosity among low-mass members being likely due to the presence of binaries and relatively rapid rotators. However, the list of X-ray selected candidate members is likely biased against low-mass, slowly rotating single stars. While some preliminary spectroscopic information is given in an appendix, further spectroscopic observations of the new candidate members will aid in interpreting the coronal activity among solar-type NGC 6475 members and their relation to similar stars in older and younger open clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/147/138
- Title:
- Rotational and radial velocities of red giants
- Short Name:
- J/AJ/147/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study presents the rotational distribution of red giant (RG) stars in 11 old to intermediate age open clusters. The masses of these stars are all above the Kraft break, so they lose negligible amounts of their birth angular momentum (AM) during the main-sequence (MS) evolution. However, they do span a mass range with quite different AM distributions imparted during formation, with the stars less massive than ~1.6M_{sun}_ arriving on the MS with lower rotation rates than the more massive stars. The majority of RGs in this study are slow rotators across the entire red giant branch regardless of mass, supporting the picture that intermediate-mass stars rapidly spin down when they evolve off the MS and develop convection zones capable of driving a magnetic dynamo. Nevertheless, a small fraction of RGs in open clusters show some level of enhanced rotation, and faster rotators are as common in these clusters as in the field RG population. Most of these enhanced rotators appear to be red clump stars, which is also true of the underlying stellar sample, while others are clearly RGs that are above or below the clump. In addition to rotational velocities, the radial velocities (RVs) and membership probabilities of individual stars are also presented. Cluster heliocentric RVs for NGC 6005 and Pismis 18 are reported for the first time.