- 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.
Number of results to display per page
Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/156/275
- Title:
- Rotational evolution of young, binary M dwarfs
- Short Name:
- J/AJ/156/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed K2 light curves for more than 3000 low-mass stars in the ~8 Myr old Upper Sco association, the ~125 Myr age Pleiades open cluster, and the ~700 Myr old Hyades and Praesepe open clusters to determine stellar rotation rates. Many of these K2 targets show two distinct periods, and for the lowest-mass stars in these clusters, virtually all of these systems with two periods are photometric binaries. The most likely explanation is that we are detecting the rotation periods for both components of these binaries. We explore the evolution of the rotation rate in both components of photometric binaries relative to one another and to nonphotometric binary stars. In Upper Sco and the Pleiades, these low-mass binary stars have periods that are much shorter on average and much closer to each other than would be true if drawn at random from the M dwarf single stars. In Upper Sco, this difference correlates strongly with the presence or absence of infrared excesses due to primordial circumstellar disks-the single-star population includes many stars with disks, and their rotation periods are distinctively longer on average than their binary star cousins of the same mass. By Praesepe age, the significance of the difference in rotation rate between the single and binary low-mass M dwarf stars is much less, suggesting that angular momentum loss from winds for fully convective zero-age main-sequence stars erases memory of the rotation rate dichotomy for binary and single very low mass stars at later ages.
866. Rotational tracks
- ID:
- ivo://CDS.VizieR/J/ApJ/776/67
- Title:
- Rotational tracks
- Short Name:
- J/ApJ/776/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar rotation is a strong function of both mass and evolutionary state. Missions such as Kepler and CoRoT provide tens of thousands of rotation periods, drawn from stellar populations that contain objects at a range of masses, ages, and evolutionary states. Given a set of reasonable starting conditions and a prescription for angular momentum loss, we address the expected range of rotation periods for cool field stellar populations (~0.4-2.0M_{sun}_). We find that cool stars fall into three distinct regimes in rotation. Rapid rotators with surface periods less than 10 days are either young low-mass main sequence (MS) stars, or higher mass subgiants which leave the MS with high rotation rates. Intermediate rotators (10-40 days) can be either cool MS dwarfs, suitable for gyrochronology, or crossing subgiants at a range of masses. Gyrochronology relations must therefore be applied cautiously, since there is an abundant population of subgiant contaminants. The slowest rotators, at periods greater than 40 days, are lower mass subgiants undergoing envelope expansion. We identify additional diagnostic uses of rotation periods. There exists a period-age relation for subgiants distinct from the MS period-age relations. There is also a period-radius relation that can be used as a constraint on the stellar radius, particularly in the interesting case of planet host stars. The high-mass/low-mass break in the rotation distribution on the MS persists onto the subgiant branch, and has potential as a diagnostic of stellar mass. Finally, this set of theoretical predictions can be compared to extensive datasets to motivate improved modeling.
- ID:
- ivo://CDS.VizieR/J/ApJ/648/580
- Title:
- Rotational velocities in 19 open clusters
- Short Name:
- J/ApJ/648/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters offer us the means to study stellar properties in samples with well-defined ages and initial chemical composition. Here we present a survey of projected rotational velocities for a large sample of mainly B-type stars in young clusters to study the time evolution of the rotational properties of massive stars. The survey is based on moderate-resolution spectra made with the WIYN 3.5m and CTIO 4m telescopes and Hydra multi-object spectrographs, and the target stars are members of 19 young open clusters with an age range of approximately 673Myr. We made fits of the observed lines HeI {lambda}{lambda}4026, 4387, 4471, and MgII {lambda}4481, using model theoretical profiles to find projected rotational velocities for a total of 496 OB stars.
- ID:
- ivo://CDS.VizieR/J/AJ/150/41
- Title:
- Rotational velocities of 136 B stars from ALS
- Short Name:
- J/AJ/150/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined projected rotational velocities, vsini, from Magellan/MIKE echelle spectra for a sample of 136 early B-type stars having large Galactocentric distances. The target selection was done independently of their possible membership in clusters, associations or field stars. We subsequently examined the literature and assigned each star as Field, Association, or Cluster. Our vsini results are consistent with a difference in aggregate vsini with stellar density. We fit bimodal Maxwellian distributions to the Field, Association, and Cluster subsamples representing sharp-lined and broad-lined components. The first two distributions, in particular, for the Field and Association are consistent with strong bimodality in vsini. Radial velocities are also presented, which are useful for further studies of binarity in B-type stars, and we also identify a sample of possible new double-lined spectroscopic binaries. In addition, we find 18 candidate Be stars showing emission at H{alpha}.
- ID:
- ivo://CDS.VizieR/J/AJ/132/749
- Title:
- Rotational velocities of O stars in clusters
- Short Name:
- J/AJ/132/749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study aimed at assessing whether low and high-mass stars form similarly. Our approach is (1) to examine the observed projected rotational velocities among a large sample of newly formed stars spanning a range in mass between 0.2 and 50M_{sun}_ and (2) to search for evidence of a discontinuity in rotational properties that might indicate a difference in the stellar formation process at some characteristic mass. Our database includes recently published values of vsini for young intermediate and low-mass stars in Orion, as well as new observations of O stars located in young clusters and OB associations.
- ID:
- ivo://CDS.VizieR/J/AJ/138/963
- Title:
- Rotation of NGC 2264 members
- Short Name:
- J/AJ/138/963
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the distance to the open cluster NGC 2264 using a statistical analysis of cluster member inclinations. We derive distance-dependent values of sini (where i is the inclination angle) for 97 stars in NGC 2264 from the rotation periods, luminosities, effective temperatures, and projected equatorial rotation velocities, vsini, measured for these stars. We have measured 96 of the vsini values in our sample by analyzing high-resolution spectra with a cross-correlation technique. We model the observed distribution of sin i for the cluster by assuming that member stars have random axial orientations and by adopting prescriptions for the measurement errors in our sample. By adjusting the distance assumed in the observed sini distribution until it matches the modeled distribution, we obtain a best-fit distance for the cluster. We find the data to be consistent with a distance to NGC 2264 of 913pc.
