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- ID:
- ivo://CDS.VizieR/J/other/Sci/292.698
- Title:
- Candidate halo dark matter
- Short Name:
- J/other/Sci/292.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Milky Way galaxy contains a large, spherical component which is believed to harbor a substantial amount of unseen matter. Recent observations indirectly suggest that as much as half of this "dark matter" may be in the form of old, very cool white dwarfs, the remnants of an ancient population of stars as old as the galaxy itself. We conducted a survey to find faint, cool white dwarfs with large space velocities, indicative of their membership in the galaxy's spherical halo component. The survey reveals a substantial, directly observed population of old white dwarfs, too faint to be seen in previous surveys. This newly discovered population accounts for at least 2 percent of the halo dark matter. It provides a natural explanation for the indirect observations, and represents a direct detection of galactic halo dark matter.
- ID:
- ivo://CDS.VizieR/J/ApJ/626/272
- Title:
- Cep A X-Ray sources
- Short Name:
- J/ApJ/626/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of X-rays from both components of Cepheus A, East and West, with the XMM-Newton observatory. HH 168 joins the ranks of other energetic Herbig-Haro objects that are sources of T>=10^6^K X-ray emission. We detect 102 X-ray sources, many presumed to be premain-sequence stars on the basis of the reddening of their optical and IR counterparts.
- ID:
- ivo://CDS.VizieR/J/A+AS/109/487
- Title:
- Color-magnitude study of M 22
- Short Name:
- J/A+AS/109/487
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new photographic C-M diagram for the globular cluster M 22 based on automatic plate measurements has been obtained. It reaches the main sequence turn-off at V=~17.1mag, (B-V)=~0.75.
- ID:
- ivo://CDS.VizieR/J/A+AS/139/231
- Title:
- Early-type stars towards the Galactic Centre
- Short Name:
- J/A+AS/139/231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have begun a search for early-type stars towards the galactic centre which are potentially young objects situated within the inner few kiloparsecs of the disk. U and V (or I) band photographic photometry from the UK Schmidt Telescope has been obtained to identify the bluest candidates in nineteen Schmidt fields (centred close to the galactic centre). We have spectroscopically observed these targets for three fields with the FLAIR multi-fibre system to determine their spectral types. In particular, ten early B-type stars have been identified and equivalent width measurements of their Balmer and HeI lines have been used to estimate atmospheric parameters. These early-type objects have magnitudes in the range 11.5=<V<=16.0, and our best estimates of their distance (given probable highly variable reddening in this direction together with errors in the plate photometry) suggest that some of them originated close to (i.e R_g_<3kpc), or even beyond the galactic centre. Future high-resolution spectroscopy of these stars will provide reliable atmospheric parameters and element abundances, in order to map the current chemical composition of the inner galaxy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/370/1034
- Title:
- FIRST-APM-SDSS survey for high-z radio QSOs
- Short Name:
- J/MNRAS/370/1034
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected from the VLA FIRST survey a sample of 94 objects with star-like counterparts in the Sloan Digital Sky Survey (SDSS), and with APM POSS-I colour O-E>=2, i.e. consistent with their being high-redshift quasars. 78 of the 94 candidates can be classified spectroscopically on the basis of either published data (mainly SDSS) or the observations presented here. The fractions of QSOs (51 out of 78) and redshift z>3 QSOs (23 out of 78, 29 per cent) are comparable to those found in other photometric searches for high-redshift QSOs. We confirm that selecting colour O-E>=2 ensures inclusion of all QSOs with 3.7<=z<=4.4. The fraction of 2<=z<=4.4 QSOs with broad absorption lines (BALs) is 27+/-10 per cent (7/26) and the estimated BAL fraction for radio-loud QSOs is at least as high as for optically selected QSOs (~13 per cent). Both the high BAL fraction and the high fraction of low-ionization BALs among BALs (four to five out of seven) in our sample, compared to previous work, are likely due to the red colour selection O-E>=2.
- ID:
- ivo://CDS.VizieR/J/ApJ/607/60
- Title:
- FIRST-2MASS faint sources
- Short Name:
- J/ApJ/607/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have constructed a sample of bright near-infrared sources that are detected at radio wavelengths but undetected on the first-generation Palomar Observatory Sky Survey (POSSI) plates in order to search for a population of dust-obscured quasars. Optical and infrared spectroscopic follow-up of the sample has led to the discovery of 17 heavily reddened quasars (B-K>6.5), 14 of which are reported here for the first time. This has allowed us to define a region in the R-K, J-K color plane in which 50% of the radio-selected objects are highly reddened quasars. We compare the surface density of this previously overlooked population to that of ultraviolet-excess radio-selected quasars, finding that they make up ~20% of the total quasar population for K<~15.5.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A42
- Title:
- Flares in 5 open clusters
- Short Name:
- J/A+A/645/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. But before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. This work sets out to quantify flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Drawing from the complete K2 archive, we searched 3435 80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690Myr) to the sample as a comparison cluster to Praesepe (750Myr), the 2.6Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with an exponent between 1.84 and 2.39. We confirmed that flaring rates declined with age, and declined faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may hint at limitations of using rotation as an age indicator without additional constraints from stellar activity.
- ID:
- ivo://CDS.VizieR/I/346
- Title:
- FON Astrographic Catalogue Southern Part (FONAC-S)
- Short Name:
- I/346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog of positions and B-magnitudes of stars and galaxies of the southern sky (from -20{deg} to +2{deg}) was created as a part of the FON (Russian abbreviation Photographic Sky Survey) project at the Ulugh Beg Astronomical Institute (UBAI) of the Uzbekistan Academy of Sciences. The data accumulated in the Photographic Archive of the UBAI were used. The total number of processed plates is 1963. Astronegatives were digitized with Epson Expression 10000XL scanners in the 1200 dpi scanning mode. The majority of plates have a size of 30x30cm. The catalog contains the data on 13 413 268 stars and galaxies with B<=17.5m at the epoch of 1984.97. The coordinates of stars and galaxies were obtained in the Tycho-2 reference system, and B-magnitudes were determined in the system of photoelectric standards. The mean internal errors of the catalog are {sigma}_RA,DE_=0.23" and {sigma}_B_=0.15mag for all objects or {sigma}_RA,DE_=0.085" and {sigma}_B_=0.054mag for the objects in the B=7-14mag range. The convergence between the catalog and Tycho-2 is characterized by the following values: 0.042" and 0.16m. The mean-square difference in coordinates from the catalog and from UCAC-4 is {sigma}_RA,DE_=0.26" (9 892 697 objects, or 73.75% of stars and galaxies, were identified).
- ID:
- ivo://CDS.VizieR/I/342
- Title:
- FON Astrographic Catalogue, Version 3.0
- Short Name:
- I/342
- Date:
- 05 Nov 2021
- Publisher:
- CDS
- Description:
- The catalog of equatorial coordinates {alpha} and {delta} and B-magnitudes of stars of the northern sky (from -4{deg} to +90{deg}) was created as a part of the FON project at the Main Astronomical Observatory of the National Academy of Sciences of Ukraine. The data accumulated in the Joint Digital Archive of the Ukrainian Virtual Observatory were used. The total number of processed plates is 2260. Astronegatives were digitized with Microtek ScanMaker 9800XL TMA and Epson Expression 10000XL scanners in the 1200 dpi scanning mode. The majority of plates have a size of 30x30cm (13000x13000-pixels). The catalog contains the data on 19451751 stars and galaxies with B<=16.5m at the epoch of 1988.1. The coordinates of stars and galaxies were obtained in the Tycho-2 reference system, and B-magnitudes were determined in the system of photoelectric standards. The mean internal errors of the catalog are {simag}_RA,DE_=0.23" and {sigma}_B_=0.14mag for all objects or {simag}_RA,DE_=0.10" and {sigma}_B_=0.07mag for stars in the B=7-14mag range. The convergence between the catalog and Tycho-2 is characterized by the following values: 0.06" and 0.15m. The mean-square difference in coordinates from the catalog and from UCAC-4 is {simag}_RA,DE_= 0.30" (18 742 932 objects, or 96.36% of stars and galaxies, were cross-identified).
