- ID:
- ivo://CDS.VizieR/J/MNRAS/429/903
- Title:
- New brown dwarf discs in Upper Scorpius
- Short Name:
- J/MNRAS/429/903
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a census of the disc population for UKIDSS selected brown dwarfs in the 5-10Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the Wide-Field Infrared Survey Explorer data base. The resulting colour-magnitude and colour-colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with discs (class II) and without discs (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This disc fraction (27 out of 116, or 23%) among brown dwarfs was found to be similar to results for K/M stars in Upper Scorpius, suggesting that the lifetimes of discs are independent of the mass of the central object for low-mass stars and brown dwarfs. 5 out of 27 discs (19%) lack excess at 3.4 and 4.6{mu}m and are potential transition discs (i.e. are in transition from class II to class III). The transition disc fraction is comparable to low-mass stars. We estimate that the time-scale for a typical transition from class II to class III is less than 0.4Myr for brown dwarfs. These results suggest that the evolution of brown dwarf discs mirrors the behaviour of discs around low-mass stars, with disc lifetimes of the order of 5-10Myr and a disc clearing time-scale significantly shorter than 1Myr.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3490
- Title:
- 15 new brown dwarfs in Orion OB1a/25 Ori group
- Short Name:
- J/MNRAS/450/3490
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of 15 new brown dwarfs belonging to the ~7Myr old 25 Orionis group and Orion OB1a subassociation with spectral types between M6 and M9 and estimated masses between ~0.07 and ~0.01M_{sun}_. By comparing them through a Bayesian method with low-mass stars (0.8<~M/M_{sun}_ <~0.1) from previous works in the 25 Orionis group, we found statistically significant differences in the number fraction of classical T Tauri stars, Weak T Tauri stars, class II, evolved discs and purely photospheric emitters at both sides of the substellar mass limit. Particularly, we found a fraction of 3.9^+2.4^_-1.6_ percent low-mass stars classified as Classic T Tauri star and class II or evolved discs, against a fraction of 33.3^+10.8^_-9.8_ percent in the substellar mass domain. Our results support the suggested scenario in which the dissipation of discs is less efficient for decreasing mass of the central object.
- ID:
- ivo://CDS.VizieR/J/MNRAS/418/1231
- Title:
- New brown dwarfs in upper Sco
- Short Name:
- J/MNRAS/418/1231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the results of a search for brown dwarfs in the Upper Scorpius Association using data from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey. Candidate young brown dwarfs were first chosen by their position in colour magnitude diagrams with further selection based on proper motions to ensure Upper Scorpius membership. Proper motions were derived by comparing UKIDSS and Two Micron All Sky Survey (2MASS) data. Using that method we identify 19 new brown dwarfs in the southern part of the association. In addition there are up to eight likely members with slightly higher dispersion velocity. The ratio of brown dwarfs to stars was found to be consistent with other areas in Upper Scorpius. It was also found to be similar to other results from young clusters with OB associations, and lower than those without, suggesting the brown dwarf formation rate may be a function of environment.
- ID:
- ivo://CDS.VizieR/J/AJ/143/84
- Title:
- New candidate globular clusters in NGC 5128
- Short Name:
- J/AJ/143/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used new wide-field imaging with the Magellan IMACS camera to search for globular cluster (GC) candidates around NGC 5128, the nearest giant E galaxy. The imaging data are in the B and R broadband filters and cover a 1.55 deg^2^ field centered on the galaxy, corresponding to an area about 90*90kpc^2^ at the distance of NGC 5128. All the fields were taken under exceptionally high-quality seeing conditions (FWHM=0.4-0.5" in R). Using this material we are able, for the first time in the literature, to construct a homogeneous list of GC candidates covering a wide span of the NGC 5128 halo and unusually free of field contaminants (foreground stars and faint background galaxies). Selecting the measured objects by color, magnitude, ellipticity, and profile size gives us a final catalog of 833 new high-quality GC candidates brighter than R=21 (0.8mag fainter than the standard GC luminosity function turnover point). The measured positions have better than 0.2" precision in both coordinates.
- ID:
- ivo://CDS.VizieR/J/A+A/590/A13
- Title:
- New candidate members in young associations
- Short Name:
- J/A+A/590/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The young associations offer us one of the best opportunities to study the properties of young stellar and sub-stellar objects and directly image planets thanks to their proximity (<200pc) and age (5-150Myr). However, many previous works have been limited to identifying the brighter, more active members (1Msun) due to photometric survey sensitivities limiting the detections of lower-mass objects. We search the field of view of 542 previously identified members of the young associations to identify wide / extremely wide (1000-100,000au in physical separation) companions. Methods. We have combined 2MASS near-infrared photometry (J, H, K) with proper motion values (from UCAC4, PPMXL, NOMAD) to identify companions in the field of view of known members. We collated further photometry and spectroscopy from the literature and conducted our own high-resolution spectroscopic observations for a sub-sample of candidate members. This complementary information allowed us to assess the efficiency of our method. We identified 84 targets (45:0.2-1.3M_{sun}_, 17:0.08-0.2M_{sun}_, 22:<0.08M_{sun}_) in our analysis, 10 of which have been identified from spectroscopic analysis in previous young association works. For 33 of these 84 we were able to further assess their membership using a variety of properties (X-ray emission, UV excess, H{alpha}, lithium and KI equivalent widths, radial velocities, and CaH indices). We derive a success rate of 76-88% for this technique based on the consistency of these properties. Once confirmed, the targets identified in this work would significantly improve our knowledge of the lower-mass end of the young associations. Additionally, these targets would make an ideal new sample for the identification and study of planets around nearby young stars. Given the predicted sub-stellar mass of the majority of these new candidate members and their proximity, high-contrast imaging techniques would facilitate the search for new low-mass planets.
- ID:
- ivo://CDS.VizieR/J/other/RAA/15.1671
- Title:
- New carbon stars from LAMOST survey
- Short Name:
- J/other/RAA/15.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon stars are excellent kinematic tracers of galaxies and can serve as a viable standard candle, so it is worthwhile to automatically search for them in a large amount of spectra. In this paper, we apply the efficient manifold ranking algorithm to search for carbon stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) pilot survey, whose performance and robustness are verified comprehensively with four test experiments. Using this algorithm, we find a total of 183 carbon stars, and 158 of them are new findings. According to different spectral features, our carbon stars are classified as 58 C-H stars, 11 C-H star candidates, 56 C-R stars, ten C-R star candidates, 30 C-N stars, three C-N star candidates, and four C-J stars. There are also ten objects which have no spectral type because of low spectral quality, and a composite spectrum consisting of a white dwarf and a carbon star. Applying the support vector machine algorithm, we obtain the linear optimum classification plane in the J-H versus H-Ks color diagram which can be used to distinguish C-H from C-N stars with their J-H and H-Ks colors. In addition, we identify 18 dwarf carbon stars with their relatively high proper motions, and find three carbon stars with FUV detections likely have optical invisible companions by cross matching with data from the Galaxy Evolution Explorer. In the end, we detect four variable carbon stars with the Northern Sky Variability Survey, the Catalina Sky Survey and the LINEAR variability databases. According to their periods and amplitudes derived by fitting light curves with a sinusoidal function, three of them are likely semiregular variable stars and one is likely a Mira variable star.
- ID:
- ivo://CDS.VizieR/J/AJ/156/90
- Title:
- New catalog of APOGEE radial velocity standard stars
- Short Name:
- J/AJ/156/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of 18080 radial velocity (RV) standard stars selected from the APOGEE data. These RV standard stars are observed at least three times and have a median stability (3{sigma}_RV_) around 240 m/s over a time baseline longer than 200 days. They are largely distributed in the northern sky and could be extended to the southern sky by the future APOGEE-2 survey. Most of the stars are red giants (J-K_s_>=0.5) owing to the APOGEE target selection criteria. Only about 10 per cent of them are main-sequence stars. The H-band magnitude range of the stars is 7-12.5 mag with the faint limit much fainter than the magnitudes of previous RV standard stars. As an application, we show the new set of standard stars to determine the RV zero points of the RAVE, the LAMOST, and the Gaia-RVS Galactic spectroscopic surveys.
- ID:
- ivo://CDS.VizieR/J/AJ/150/27
- Title:
- New catalog of variable stars in M37 field
- Short Name:
- J/AJ/150/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive re-analysis of stellar photometric variability in the field of the open cluster M37 following the application of a new photometry and de-trending method to the MMT/Megacam image archive. This new analysis allows a rare opportunity to explore photometric variability over a broad range of timescales, from minutes to a month. The intent of this work is to examine the entire sample of more than 30000 objects for periodic, aperiodic, and sporadic behaviors in their light curves. We show a modified version of the fast {chi}^2^ periodogram algorithm (F{chi}^2^) and change-point analysis as tools for detecting and assessing the significance of periodic and non-periodic variations. The benefits of our new photometry and analysis methods are evident. A total of 2306 stars exhibit convincing variations that are induced by flares, pulsations, eclipses, starspots, and unknown causes in some cases. This represents a 60% increase in the number of variables known in this field. Moreover, 30 of the previously identified variables are found to be false positives resulting from time-dependent systematic effects. The new catalog includes 61 eclipsing binary systems, 92 multiperiodic variable stars, 132 aperiodic variables, and 436 flare stars, as well as several hundreds of rotating variables. Based on extended and improved catalog of variables, we investigate the basic properties (e.g., period, amplitude, type) of all variables. The catalog can be accessed through the web interface (http://stardb.yonsei.ac.kr/).
- ID:
- ivo://CDS.VizieR/J/AJ/134/741
- Title:
- New close binary systems from the SDSS DR5
- Short Name:
- J/AJ/134/741
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest catalog of more than 1200 spectroscopically selected close binary systems observed with the Sloan Digital Sky Survey through Data Release Five. We use the catalog to search for magnetic white dwarfs in cataclysmic variable progenitor systems. Given that approximately 25% of cataclysmic variables contain a magnetic white dwarf, and that our large sample of close binary systems should contain many progenitors of cataclysmic variables, it is quite surprising that we find only two potential magnetic white dwarfs in this sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/859
- Title:
- New companions to nearby low-mass stars
- Short Name:
- J/MNRAS/429/859
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-angular-resolution optical I-band imaging of 451 late K to mid-M nearby stars. These observations have been performed with Astralux and FastCam using the lucky imaging technique. We found 70 companions with separations between 0.1 and 3.5-arcsec, out of which 28 are new discoveries. We derive a total binary fraction of 20.3^+6.9^_-5.2_ per cent. Follow-up observations have been carried out for 16 of these new binaries and all of them were confirmed as physically associated systems. Parallaxes are available for 70 per cent of the binary sample, providing reliable estimates of physical separations. We have measured separations and position angles as an initial stage for a systematic follow-up aimed to determine orbital parameters.