- ID:
- ivo://CDS.VizieR/J/AJ/150/16
- Title:
- Speckle-interferometry in Melotte 111
- Short Name:
- J/AJ/150/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high-angular resolution survey for the search of binary and multiple stars in the Galactic open cluster Melotte 111. Combining our own speckle-interferometric observations with data taken from the literature, we found a ratio of the number of single to multiple stars to be 29:8:0:0:0:1 for the most probable members, indicating a multiplicity fraction for this cluster of 25.6%+/-2%. We also observed field stars in the vicinity of the cluster and estimated a ratio of multiplicities of 286:17:1:0:0:0:1 (between one and seven companions), equivalent to a multiplicity fraction of 5.9%+/-3%. We showed that the cumulative distribution of separations for our sample stars is in agreement with Opik's law.
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- ID:
- ivo://CDS.VizieR/J/AJ/162/156
- Title:
- Speckle interfero. nearby multiple stars. II
- Short Name:
- J/AJ/162/156
- Date:
- 14 Mar 2022 06:50:24
- Publisher:
- CDS
- Description:
- Long-term monitoring at the 6m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences made it possible to improve the orbits of 15 objects (HIP689, HIP3951, HIP10438, HIP43948, HIP69962, HIP95995, HIP102029, HIP102357, HIP104383, HIP105947, HIP106255, HIP108917, HIP111546, HIP113726, HIP114922) and construct an orbital solution for HIP65327 for the first time. Observations have been carried out since 2007; that is, the accumulated data correspond to an interval of 13yr. As a result, most of the orbits were classified as "accurate" using the qualitative criteria by Worley & Heintz. A comparison of the mass sums and masses of the components calculated by two independent methods was made for objects with orbital solutions. The Gaia EDR3 parallax was used to obtain the fundamental parameters, as well as the Hipparcos and Gaia DR2 parallaxes.
- ID:
- ivo://CDS.VizieR/J/AJ/162/75
- Title:
- Speckle observations TESS exoplanet host stars. II.
- Short Name:
- J/AJ/162/75
- Date:
- 18 Mar 2022 09:30:45
- Publisher:
- CDS
- Description:
- We present high-angular-resolution imaging observations of 517 host stars of TESS exoplanet candidates using the 'Alopeke and Zorro speckle cameras at Gemini North and South. The sample consists mainly of bright F, G, K stars at distances of less than 500pc. Our speckle observations span angular resolutions of ~20mas out to 1.2", yielding spatial resolutions of <10-500au for most stars, and our contrast limits can detect companion stars 5-9mag fainter than the primary at optical wavelengths. We detect 102 close stellar companions and determine the separation, magnitude difference, mass ratio, and estimated orbital period for each system. Our observations of exoplanet host star binaries reveal that they have wider separations than field binaries, with a mean orbital semimajor axis near 100 au. Other imaging studies have suggested this dearth of very closely separated binaries in systems which host exoplanets, but incompleteness at small separations makes it difficult to disentangle unobserved companions from a true lack of companions. With our improved angular resolution and sensitivity, we confirm that this lack of close exoplanet host binaries is indeed real. We also search for a correlation between planetary orbital radii versus binary star separation; but, given the very short orbital periods of the TESS planets, we do not find any clear trend. We do note that in exoplanet systems containing binary host stars, there is an observational bias against detecting Earth-size planet transits due to transit depth dilution caused by the companion star.
- ID:
- ivo://CDS.VizieR/J/A+A/546/A9
- Title:
- Spectral classification of stars in NGC 6530
- Short Name:
- J/A+A/546/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mechanisms involved in the star formation process and in particular the duration of the different phases of the cloud contraction are not yet fully understood. Photometric data alone suggest that objects coexist in the young cluster NGC 6530 with ages from ~1Myr up to 10Myrs. We want to derive accurate stellar parameters and, in particular, stellar ages to be able to constrain a possible age spread in the star-forming region NGC6530.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1239
- Title:
- Spectral distances to DA white dwarfs
- Short Name:
- J/AJ/135/1239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using recent photometric calibrations, we develop greatly improved distance estimates for DA white dwarfs using multi-band synthetic photometry based on spectroscopic temperatures and gravities. Very good correlations are shown to exist between our spectroscopically based photometric distance estimates and those derived from trigonometric parallaxes. We investigate the uncertainties involved in our distance estimates, as well as discuss the circumstances where such techniques are most likely to fail. We apply our techniques to the large sample of Sloan Digital Sky Survey DA white dwarfs where automated fitting of HI Balmer profiles yields spectrometric temperatures and gravities. We determine simple empirical corrections to these temperatures and gravities with respect to published slit spectroscopy. After applying these T_eff_-logg corrections as well as appropriate interstellar extinction corrections, where necessary, we derive spectroscopically based photometric distances for 7062 DA stars from this sample.
- ID:
- ivo://CDS.VizieR/J/ApJS/224/26
- Title:
- Spectral energy distributions of Roma BZCAT blazars
- Short Name:
- J/ApJS/224/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combined multi-wavelength data for blazars from the Roma-BZCAT catalog and analyzed hundreds of X-ray spectra. We present the fluxes and spectral energy distributions (SEDs), in 12 frequency bands from radio to {gamma}-rays, for a final sample of 2214 blazars. Using a model-independent statistical approach, we looked for systematic trends in the SEDs; the most significant trends involved the radio luminosities and X-ray spectral indices of the blazars. We used a principal component analysis (PCA) to determine the basis vectors of the blazar SEDs and, in order to maximize the size of the sample, imputed missing fluxes using the K-nearest neighbors method. Using more than an order of magnitude more data than was available when Fossati et al. first reported trends of SED shape with blazar luminosity, we confirmed the anti-correlation between radio luminosity and synchrotron peak frequency, although with greater scatter than was seen in the smaller sample. The same trend can be seen between bolometric luminosity and synchrotron peak frequency. Finally, we used all of the available blazar data to determine an empirical SED description that depends only on the radio luminosity at 1.4GHz and the redshift. We verified that this statistically significant relation was not a result of the luminosity-luminosity correlations that are natural in flux-limited samples (i.e., where the correlation is actually caused by the redshift rather than the luminosity).
2077. Spectra of T dwarfs. I.
- ID:
- ivo://CDS.VizieR/J/ApJ/564/421
- Title:
- Spectra of T dwarfs. I.
- Short Name:
- J/ApJ/564/421
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared spectra for a sample of T dwarfs, including 11 new discoveries made using the 2 Micron All Sky Survey. These objects are distinguished from warmer (L-type) brown dwarfs by the presence of methane absorption bands in the 1-2.5{mu}m spectral region. A first attempt at a near-infrared classification scheme for T dwarfs is made, based on the strengths of CH_4_ and H_2_O bands and the shapes of the 1.25, 1.6, and 2.1{mu}m flux peaks. Subtypes T1 VT8 V are defined, and spectral indices useful for classification are presented.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/705
- Title:
- Spectrophotometric distances of HII regions
- Short Name:
- J/MNRAS/411/705
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a near-infrared study of the stellar content of 35 HII regions in the Galactic plane, 24 of which have been classified as giant H ii regions. We have selected these optically obscured star-forming regions from the catalogues of Russeil (2003, Cat. J/A+A/397/133), Conti & Crowther (2004MNRAS.355..899C) and Bica et al. (2003, Cat. J/A+A/404/223). In this paper, we have used the near-infrared domain J-, H- and Ks-band colour images to visually inspect the sample. Also, we have used colour-colour and colour-magnitude diagrams to indicate ionizing star candidates, as well as the presence of young stellar objects such as classical T Tauri stars and massive young stellar objects (MYSOs). We have obtained Spitzer Infrared Array Camera images for each region to help further characterize them. Spitzer and near-infrared morphology were used to place each cluster in an evolutionary phase of development. Spitzer photometry was also used to classify the MYSOs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/501/2848
- Title:
- Spectrophotometric standard cand. photometry
- Short Name:
- J/MNRAS/501/2848
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Johnson-Kron-Cousins BVRI photometry of 228 candidate spectrophotometric standard stars for the external (absolute) flux calibration of Gaia data. The data were gathered as part of a 10-yr observing campaign with the goal of building the external grid of flux standards for Gaia and we obtained absolute photometry, relative photometry for constancy monitoring, and spectrophotometry. Preliminary releases of the flux tables were used to calibrate the first two Gaia releases. This paper focuses on the imaging frames observed in good sky conditions (about 9100). The photometry will be used to validate the ground-based flux tables of the Gaia spectrophotometric standard stars and to correct the spectra obtained in non-perfectly photometric observing conditions for small zero-point variations. The absolute photometry presented here is tied to the Landolt standard stars system to ~1 per cent or better, depending on the photometric band. Extensive comparisons with various literature sources show an overall ~1 per cent agreement, which appears to be the current limit in the accuracy of flux calibrations across various samples and techniques in the literature. The Gaia photometric precision is presently of the order of 0.1 per cent or better, thus various ideas for the improvement of photometric calibration accuracy are discussed.
- ID:
- ivo://CDS.VizieR/J/AJ/147/16
- Title:
- Spectroscocpy of planetary nebulae in M31
- Short Name:
- J/AJ/147/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed a method to identify planetary nebula (PN) candidates in imaging data of the Sloan Digital Sky Survey (SDSS). This method exploits the SDSS's five-band sampling of emission lines in PN spectra, which results in a color signature distinct from that of other sources. Selection criteria based on this signature can be applied to nearby galaxies in which PNe appear as point sources. We applied these criteria to the whole area of M31 as scanned by the SDSS, selecting 167 PN candidates that are located in the outer regions of M31. The spectra of 80 selected candidates were then observed with the 2.2m telescope at Calar Alto Observatory. These observations and cross-checks with literature data show that our method has a selection rate efficiency of about 90%, but the efficiency is different for the different groups of PN candidates. In the outer regions of M31, PNe trace different well-known morphological features like the Northern Spur, the NGC 205 Loop, the G1 Clump, etc. In general, the distribution of PNe in the outer region 8<R<20kpc along the minor axis shows the "extended disk"-a rotationally supported low surface brightness structure with an exponential scale length of 3.21+/-0.14kpc and a total mass of ~10^10^M_{sun}_, which is equivalent to the mass of M33. We report the discovery of three PN candidates with projected locations in the center of Andromeda NE, a very low surface brightness giant stellar structure in the outer halo of M31. Two of the PNe were spectroscopically confirmed as genuine PNe. These two PNe are located at projected distances along the major axis of ~48Kpc and ~41Kpc from the center of M31 and are the most distant PNe in M31 found up to now. With the new PN data at hand we see the obvious kinematic connection between the continuation of the Giant Stream and the Northern Spur. We suggest that 20%-30% of the stars in the Northern Spur area may belong to the Giant Stream. In our data we also see a possible kinematic connection between the Giant Stream and PNe in Andromeda NE, suggesting that Andromeda NE could be the core or remnant of the Giant Stream. Using PN data we estimate the total mass of the Giant Stream progenitor to be {approx}10^9^M_{sun}_. About 90% of its stars appear to have been lost during the interaction with M31.
