- ID:
- ivo://CDS.VizieR/J/AJ/151/166
- Title:
- Stellar flares and variables from 2009-2010 CSTAR
- Short Name:
- J/AJ/151/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chinese Small Telescope Array (CSTAR) carried out high-cadence time-series observations of ~20.1 square degrees centered on the South Celestial Pole during the 2008, 2009, and 2010 winter seasons from Dome A in Antarctica. The nearly continuous six months of dark conditions during each observing season allowed for >10^6^ images to be collected through gri and clear filters, resulting in the detection of >10^4^ sources over the course of three years of operation. The nearly space-like conditions in the Antarctic plateau are an ideal testbed for the suitability of very small-aperture (<20cm) telescopes to detect transient events, variable stars, and stellar flares. We present the results of a robust search for such objects using difference image analysis of the data obtained during the 2009 and 2010 winter seasons. While no transients were found, we detected 29 flaring events and find a normalized flaring rate of 5+/-4*10^-7^flare/hr for late-K dwarfs, 1+/-1*10^-6^flare/hr for M dwarfs and 7+/-1*10^-7^flare/hr for all other stars in our sample. We suggest future small-aperture telescopes planned for deployment at Dome A would benefit from a tracking mechanism, to help alleviate effects from ghosting, and a finer pixel scale, to increase the telescope's sensitivity to faint objects. We find that the light curves of non-transient sources have excellent photometric qualities once corrected for systematics, and are limited only by photon noise and atmospheric scintillation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/435
- Title:
- Stellar parameters and extinction
- Short Name:
- J/MNRAS/411/435
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrometric surveys provide the opportunity to measure the absolute magnitudes of large numbers of stars, but only if the individual line-of-sight extinctions are known. Unfortunately, extinction is highly degenerate with stellar effective temperature when estimated from broad band optical/infrared photometry. To address this problem, I introduce a Bayesian method for estimating the intrinsic parameters of a star and its line-of-sight extinction.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/1153
- Title:
- Stellar parameters of giants in {omega} Cen
- Short Name:
- J/MNRAS/427/1153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined stellar parameters and abundances for 221 giant branch stars in the globular cluster omega Centauri. A combination of photometry and lower-resolution spectroscopy was used to determine temperature, gravity, metallicity, [C/Fe], [N/Fe] and [Ba/Fe]. These abundances agree well with those found by previous researchers and expand the analysed sample of the cluster. k-means clustering analysis was used to group the stars into four homogeneous groups based upon these abundances. These stars show the expected anticorrelation in [C/Fe] to [N/Fe]. We investigated the distribution of CN-weak/strong stars on the colour-magnitude diagram. Asymptotic giant branch stars, which were selected from their position on the colour-magnitude diagram, were almost all CN-weak. This is in contrast to the red giant branch where a large minority were CN-strong. The results were also compared with cluster formation and evolution models. Overall, this study shows that statistically significant elemental and evolutionary conclusions can be obtained from lower resolution spectroscopy.
- ID:
- ivo://CDS.VizieR/II/237
- Title:
- Stellar Photometry in Johnson's 11-color system
- Short Name:
- II/237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue gives photometric data in the UBVRIJHKLMN colors and some additional information. Data for the JHKLMN bands come from NASA Ref. Pub. 1294 (1993). More complete information is found in Wisconsin Astrophysics 504 (1993) The effective wavelength of the Johsnon filters are: U = 360 nm B = 450 nm V = 555 nm R = 670 nm I = 870 nm J = 1.2 um H = 1.62um K = 2.2 um L = 3.5 um M = 5.0 um N = 9.0 um
- ID:
- ivo://CDS.VizieR/J/AJ/161/288
- Title:
- Stellar population in M53
- Short Name:
- J/AJ/161/288
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at ~3800 and 4300{AA}, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify five CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na-O anticorrelation and pseudo-color indices in Hubble Space Telescope UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters, CN-enhanced stars have a slightly enhanced C+N+O ({Delta}(C+N+O)~0.2dex).
- ID:
- ivo://CDS.VizieR/J/AJ/154/87
- Title:
- Stellar population of the young star cluster NGC 6231
- Short Name:
- J/AJ/154/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6231 is a young cluster (age ~2-7 Myr) dominating the Sco OB1 association (distance ~1.59 kpc) with ~100 O and B stars and a large pre-main-sequence stellar population. We combine a reanalysis of archival Chandra X-ray data with multiepoch near-infrared (NIR) photometry from the VISTA Variables in the Via Lactea (VVV) survey and published optical catalogs to obtain a catalog of 2148 probable cluster members. This catalog is 70% larger than previous censuses of probable cluster members in NGC 6231. It includes many low-mass stars detected in the NIR but not in the optical and some B stars without previously noted X-ray counterparts. In addition, we identify 295 NIR variables, about half of which are expected to be pre-main-sequence stars. With the more complete sample, we estimate a total population in the Chandra field of 5700-7500 cluster members down to 0.08 M_{sun}_ (assuming a universal initial mass function) with a completeness limit at 0.5 M_{sun}_. A decrease in stellar X-ray luminosities is noted relative to other younger clusters. However, within the cluster, there is little variation in the distribution of X-ray luminosities for ages less than 5 Myr. The X-ray spectral hardness for B stars may be useful for distinguishing between early-B stars with X-rays generated in stellar winds and B-star systems with X-rays from a pre-main-sequence companion (>35% of B stars). A small fraction of catalog members have unusually high X-ray median energies or reddened NIR colors, which might be explained by absorption from thick or edge-on disks or being background field stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/695/679
- Title:
- Stellar rotation in M35
- Short Name:
- J/ApJ/695/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a five month photometric time-series survey for stellar rotation over a 40'x40' field centered on the 150Myr open cluster M35 (=NGC 2168). We report rotation periods for 441 stars within this field and determine their cluster membership and binarity based on a decade-long radial velocity survey, proper-motion measurements, and multiband photometric observations. We find that 310 of the stars with measured rotation periods are late-type members of M35. The distribution of rotation periods for cluster members span more than 2 orders of magnitude from ~0.1 to 15 days, not constrained by the sampling frequency and the timespan of the survey. With an age between the zero-age main sequence and the Hyades, and with ~6 times more rotation periods than measured in the Pleiades, M35 permit detailed studies of early rotational evolution of late-type stars. Nearly 80% of the 310 rotators lie on two distinct sequences in the color-period plane, and define clear relations between stellar rotation period and color (mass). The M35 color-period diagram enables us to determine timescales for the transition between the two rotational states, of ~60Myr and ~140Myr for G and K dwarfs, respectively.
- ID:
- ivo://CDS.VizieR/J/PASP/114/656
- Title:
- Stellar variability in field stars
- Short Name:
- J/PASP/114/656
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a 5 night wide-field time-series photometric survey that detects variable field stars. We find that the fraction of stars whose light curves show variations depends on color and magnitude, reaching 17% for the brightest stars in this survey (V~4) for which the photometric precision is best. The fraction of stars found to be variable is relatively high at colors bluer than the Sun and relatively low at colors similar to the Sun and increases again for stars redder than the Sun. We present light curves for a sample of the pulsating and eclipsing variables. Most of the stars identified as pulsating variables have low amplitudes ({Delta}V=0.01-0.05), relatively blue colors, and multiple periods. There are 13 stars we identify as either SX Phoenicis or {delta} Scuti stars. These classes represent a significant contribution to the total number of blue variables found in this survey. Another 17 stars are identified as eclipsing variables, which have a wide range in color, magnitude, and amplitude. Two variable giants are observed, and both show night-to-night ~1% variations. We present data for 222 variables in total, most of which are not classified. Implications of surveys for stellar variability and interferometry are briefly discussed. On 2000 March 16-20 UT we observed a time series of images in V and one or two images each in UBRI toward two 59'x59' fields using the NOAO Mosaic Camera at the Kitt Peak 0.9 m telescope.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/409
- Title:
- Stock 2 CCD photometry and proper motions
- Short Name:
- J/A+AS/143/409
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the first CCD BVRI photometric and proper motion study of late-type stars in the young open cluster Stock 2. Twenty-one fields of approximately 5'x5' size have been observed photometrically, from which we have identified 118 candidate members based on their positions on colour-magnitude diagrams relative to theoretical isochrones. From a comparison of the known star density of the Pleiades, we estimate the contamination of this selection process due to background stars to be as large as ~50%. However, only 22 of those 118 candidate members have proper motions consistent with membership, suggesting that the contamination is of the order of 80%. Additional candidate members were found by means of a proper motion analysis of Schmidt plate material for a 3{deg}x3{ deg} field containing the cluster. The cluster proper motion allows us to separate members from background and foreground stars. We have found 634 stars with a membership probability >=50% down to a limiting magnitude of B=~20, corresponding to late-M dwarfs at the distance of Stock 2.
- ID:
- ivo://CDS.VizieR/J/MNRAS/439/788
- Title:
- Stromgren and Washington photometry in Boo I
- Short Name:
- J/MNRAS/439/788
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Stromgren and Washington data sets for the Bootes I dwarf galaxy, and combine them with the available Sloan Digital Sky Survey photometry. The goal of this project is to refine a ground-based, practical, accurate method to determine age and metallicity for individual stars in Bootes I that can be selected in an unbiased imaging survey, without having to take spectra. With few bright upper red giant branch stars and distances of about 35-250kpc, the ultra-faint dwarf galaxies (UDFs) present observational challenges in characterizing their stellar population. Other recent studies have produced spectra and proper motions, making Bootes I an ideal test case for our photometric methods. We produce photometric metallicities from Stromgren and Washington photometry, for stellar systems with a range of -1.0>[Fe/H]>-3.5. Needing to avoid the collapse of the metallicity sensitivity of the Stromgren m1-index on the lower red giant branch, we replace the Stromgren v filter with the broader Washington C filter to minimize observing time. We construct two indices: m*=(C-T1)0-(T1-T2)0 and m**=(C-b)0-(b-y)0. We find that CT1by is the most successful filter combination, for individual stars with [Fe/H] < -2.0, to maintain ~0.2dex [Fe/H]-resolution over the whole red giant branch. The m**-index would be the best choice for space-based observations because the (C-y) colour is not sufficient to fix metallicity alone in an understudied system. Our photometric metallicites of stars in the central regions of Bootes I confirm that there is a metallicity spread of at least -1.9>[Fe/H]>-3.7. The best-fitting Dartmouth isochrones give a mean age, for all the Bootes I stars in our data set, of 11.5+/-0.4Gyr. From ground-based telescopes, we show that the optimal filter combination is CT1by, avoiding the v filter entirely. We demonstrate that we can break the isochrones' age-metallicity degeneracy with the CT1by filters, using stars with logg=2.5-3.0, which have less than a 2percent change in their (C-T1) colour due to age, over a range of 10^-14^Gyr.
