- ID:
- ivo://CDS.VizieR/J/AJ/152/113
- Title:
- Pleiades members with K2 light curves. I. Periods
- Short Name:
- J/AJ/152/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young (125Myr), populous (>1000 members), and relatively nearby, the Pleiades has provided an anchor for stellar angular momentum models for both younger and older stars. We used K2 to explore the distribution of rotation periods in the Pleiades. With more than 500 new periods for Pleiades members, we are vastly expanding the number of Pleiades with periods, particularly at the low-mass end. About 92% of the members in our sample have at least one measured spot-modulated rotation period. For the ~8% of the members without periods, non-astrophysical effects often dominate (saturation, etc.), such that periodic signals might have been detectable, all other things being equal. We now have an unusually complete view of the rotation distribution in the Pleiades. The relationship between P and (V-K_s_)_0_ follows the overall trends found in other Pleiades studies. There is a slowly rotating sequence for 1.1<~(V-K_s_)_0_<~3.7 and a primarily rapidly rotating population for (V-K_s_)_0_>~5.0. There is a region in which there seems to be a disorganized relationship between P and (V-K_s_)_0_ for 3.7<~(V-K_s_)_0_<~5.0. Paper II continues the discussion, focusing on multiperiod structures, and Paper III speculates about the origin and evolution of the period distribution in the Pleiades.
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Search Results
- ID:
- ivo://CDS.VizieR/I/258
- Title:
- Pleiades positions and proper motions
- Short Name:
- I/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a preliminary reference catalogue, combined with the catalogues PPM, ACRS and those in Eichhorn et al (1970, Cat. <I/90>), Jones (1973A&AS....9..313J) and Hertzsprung (1947AnLei..19a...1H), 33 exposures on 11 plates taken with the Zo-Se 40cm refractor (f=6895mm) in 86 years are reduced with the central overlapping technique, and high-precision positions and proper motions of 441 stars in the Pleiades astrometric standard region are obtained. The standard errors of star positions are less than +/-0.05arcsec, and the standard errors of proper motions for 90% stars in our reduction are less than +/-0.001arcsec/yr.
- ID:
- ivo://CDS.VizieR/J/AJ/121/1040
- Title:
- PMS members of upper Scorpius OB association
- Short Name:
- J/AJ/121/1040
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a large intermediate-resolution spectroscopic survey for pre-main-sequence (PMS) stars in the Upper Scorpius OB association, the nearest region of recent massive star formation. Utilizing the 2dF multiobject spectrograph at the Anglo-Australian Telescope, we obtained spectra of 576 stars with magnitudes 12.5<=R<=16.5 in a 6{deg}^2^ area in Upper Scorpius. Among these objects we were able to identify 98 new PMS stars, nearly all of them M-type stars, by their strong lithium absorption lines. We place the new PMS stars into the H-R diagram and find that their ages agree well with the mean age of 5Myr determined in our earlier investigation based on a smaller sample of stars. The number of low-mass (0.1M_{sun}_<~M*<~0.5M_{sun}) members is at least as high as expected from the known number of high-mass (M*>~3M_{sun}_) association members and from recent determinations of the field star initial mass function. Thus, there is no deficit of low-mass stars in Upper Scorpius.
844. PMS stars in h Per
- ID:
- ivo://CDS.VizieR/J/A+A/589/A113
- Title:
- PMS stars in h Per
- Short Name:
- J/A+A/589/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several studies showed that the magnetic activity of late-type main-sequence (MS) stars is characterized by different regimes and that their activity levels are well described by the Ross by number, Ro, defined as the ratio between the rotational period P_rot_ and the convective turnover time. Very young pre-main-sequence (PMS) stars show, similarly to MS stars, intense magnetic activity. However, they do not show clear activity-rotation trends, and it still debated which stellar parameters determine their magnetic activity levels. To bridge the gap between MS and PMS stars, we studied the activity-rotation relation in the young cluster h Persei, a ~13Myr old cluster, that contains both fast and slow rotators. The cluster members have ended their accretion phase and have developed a radiative core. It therefore offers us the opportunity of studying the activity level of intermediate-age PMS stars with different rotational velocities, excluding any interactions with the circumstellar environment We constrained the magnetic activity levels of h Per members by measuring their X-ray emission from a Chandra observation, while rotational periods were obtained previously in the framework of the MONITOR project. By cross-correlating these data, we collected a final catalog of 414 h Per members with known rotational period, effective temperature, and mass. In 169 of these, X-ray emission has also been detected.
- ID:
- ivo://CDS.VizieR/J/A+A/467/1397
- Title:
- PMS stars in open clusters: the DAY-I Catalogue
- Short Name:
- J/A+A/467/1397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the basic ideas and first results from the project we are carrying out at present, the search for and characterisation of pre-main sequence (PMS) stars among the members of Galactic young clusters. The observations of 10 southern clusters, nine of them located in the Carina-Sagittarius spiral arm of the Milky Way are presented. We aim at listing candidate PMS member stars in young clusters. The catalogued stars will serve as a basis for future spectroscopic studies of individual objects to determine the properties of stellar formation in the last phases before the main sequence stage. Properties such as the presence of residual envelopes or disks, age spread among PMS members, and the possible presence of several episodes of star formation in the clusters, are to be addressed. Multicolour photometry in the UBVRcIc system has been obtained for 10 southern young clusters in the fourth Galactic quadrant, located between Galactic longitudes l=238 and l=310. For six clusters in the sample, the observations presented here provide the first published study based on CCD photometry. A quantitative comparison is performed with post-MS isochrones, and PMS isochrones from three different evolutionary models are used in the photometric membership analysis for possible PMS stars. The observations produce photometric indices in the Johnson-Cousins photometric systems for a total of 26962 stars. The matching of our pixel coordinates with corresponding fields in the 2MASS data base provides astrometric calibration for all catalogued stars and JHK 2MASS photometric indices for 60% of them. Post-MS cluster ages range from 4 to 60Myr, whereas the photometric membership analysis assigns PMS membership assignment to a total of 842 stars, covering an age range between 1 and 10Myr. This information on the PMS candidate members has been collected into a catalogue, named DAY-I, which contains 16 entries for 842 stars in the field of 10 southern clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/513/A75
- Title:
- Polarimetry of stars in NGC 5617
- Short Name:
- J/A+A/513/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present polarimetric observations in the UBVRI bands of 72 stars located in the direction of the medium age open cluster NGC 5617. Our intention is to use polarimetry as a tool in membership identification, by building on previous investigations intended mainly to determine the cluster's general characteristics rather than provide membership suitable for studies such as stellar content and metallicity, as well as study the characteristics of the dust lying between the Sun and the cluster.
- ID:
- ivo://CDS.VizieR/J/AJ/160/256
- Title:
- Polarization of 125 stars in NGC 1817 open cluster
- Short Name:
- J/AJ/160/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiband linear polarimetric observations of 125 stars in the region of the cluster NGC1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V-band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC1817. The average value of the position angle in the V-band of 119.2{deg} is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54{+/-}0.02{mu}m indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1577
- Title:
- Polarization towards open cluster NGC 6823
- Short Name:
- J/MNRAS/403/1577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is approximately located within 200pc towards the cluster, which is much closer to the Sun than the cluster itself (~2.1kpc). The radial distribution of the position angles for the member stars is found to show a systematic change, while the polarization is found to reduce towards the outer parts of the cluster and the average position angle of the coronal region of the cluster is very close to the inclination of the Galactic parallel (~32{deg}). The size distribution of the grains within NGC 6823 is similar to those in the general interstellar medium. The patchy distribution of foreground dust grains is suggested to be mainly responsible for both differential reddening and polarization towards NGC 6823. The majority of the observed stars do not show evidence of intrinsic polarization in their light.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A1
- Title:
- Portrait Galactic disc
- Short Name:
- J/A+A/640/A1
- Date:
- 28 Feb 2022 08:13:18
- Publisher:
- CDS
- Description:
- The large astrometric and photometric survey performed by the Gaia mission allows for a panoptic view of the Galactic disc and in its stellar cluster population. Hundreds of clusters were only discovered after the latest Gaia data release (DR2) and have yet to be characterised. Here we make use of the deep and homogeneous Gaia photometry down to G=18 to estimate the distance, age, and interstellar reddening for about 2000 clusters identified with Gaia DR2 astrometry. We use these objects to study the structure and evolution of the Galactic disc. We rely on a set of objects with well-determined parameters in the literature to train an artificial neural network to estimate parameters from the Gaia photometry of cluster members and their mean parallax. We obtain reliable parameters for 1867 clusters. Our new homogeneous catalogue confirms the relative lack of old clusters in the inner disc (with a few notable exceptions). We also quantify and discuss the variation of scale height with cluster age, and detect the Galactic warp in the distribution of old clusters. This work results in a large and homogenous cluster catalogue. However, the present sample is still unable to trace the Outer spiral arm of the Milky Way, which indicates that the outer disc cluster census might still be incomplete.
- ID:
- ivo://CDS.VizieR/J/A+A/491/951
- Title:
- Positions and cross-references in Coma Ber
- Short Name:
- J/A+A/491/951
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although several attempts were made to identify solar-type members on the main sequence of the nearby open cluster Coma Berenices (Mel 111), the population of the lower main sequence is still poorly known. We observed 46 new candidates to search for new members and monitored known spectroscopic-binary members to determine orbital parameters. We obtained a total of 903 radial-velocity measurements of 69 solar-type stars in the field of Mel 111 with the CORAVEL spectrovelocimeter over 20 years. Among the 35 stars from Trumpler's list, 23 are members according to their radial velocities and photometry. We were able to confirm the membership of only 8 stars among the 46 candidates observed. Six double-lined and ten single-lined spectroscopic binaries were discovered. Six only are members and an orbit was determined for them and for 4 double-lined non-members. The binary frequency is 22% (7/32). The cluster mean radial velocity is +0.01+/-0.08km/s based on 28 members. The lower main sequence of the Coma Berenices open cluster is still rather poorly populated. The cluster size may be much larger that usually accepted. Accordingly extensive programmes of precise proper motions, radial velocities and photometry should be undertaken to identify faint cluster members outside the cluster central area. If a significant population of faint members cannot be identified, Coma Ber could be a prominent example of dynamical evolution leading to star evaporation.
