- ID:
- ivo://CDS.VizieR/J/AJ/126/2421
- Title:
- 2MASS-Selected sample of ultracool dwarfs
- Short Name:
- J/AJ/126/2421
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the initial results of our effort to create a statistically robust, volume-limited sample of ultracool dwarfs from the Two Micron All Sky Survey Second Incremental Data Release (<II/241>). We are engaged in a multifaceted search for nearby late-type objects, and this is the first installment of our search using purely photometric selection. The goal of this work is a determination of the low-mass star and brown dwarf luminosity function in the infrared. Here we outline the construction of the sample, dubbed 2MU2, and present our first results, including the discovery of 186 M7-L6 dwarfs, 47 of which are likely to be within 20pc of the Sun. These results represent 66% of the ultracool candidates in our sample yet constitute a 127% increase in the number of ultracool dwarfs known within the volume searched (covering 40% of the sky out to 20pc). In addition, we have identified 10 M4-M6.5 objects that are likely to be within 20pc (or within 1{sigma}). Finally, based on these initial data, we present a preliminary luminosity function and discuss several interesting features of the partial sample presented here. Once our sample is complete, we will use our measured luminosity function to constrain the mass function of low-mass stars and brown dwarfs.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/other/RAA/15.1182
- Title:
- M Dwarf catalog of LAMOST DR1
- Short Name:
- J/other/RAA/15.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic catalog of 93 619 M dwarfs from the first data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) general survey. During sample selection, M giant contamination was eliminated using 2MASS photometry and CaH/TiO molecular indices. For each spectrum, the spectral subtype and values are provided including radial velocity, H{alpha} equivalent width, a series of prominent molecular band indices, and the metal-sensitive parameter {zeta}, as well as distances and the space motions for high S/N objects. In addition, H{alpha} emission lines are measured to examine the magnetic activity properties of M dwarfs and 7179 active ones are found. In particular, a subsample with significant variation in magnetic activity is revealed through observations from different epochs. Finally, statistical analysis for this sample is performed, including the metallicity classification, the distribution of molecular band indices and their errors.
- ID:
- ivo://CDS.VizieR/J/AJ/159/52
- Title:
- M dwarfs at high spectral-resolution in Y band
- Short Name:
- J/AJ/159/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In young Sun-like stars and field M-dwarf stars, chromospheric and coronal magnetic activity indicators such as H{alpha}, X-ray, and radio emission are known to saturate with low Rossby number (Ro<~0.1), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric TiI and CaI absorption lines in the Y band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field, or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing Ro and saturation of the equivalent widths for Ro<~0.1. The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.
- ID:
- ivo://CDS.VizieR/J/A+A/571/A36
- Title:
- M dwarfs in b201 tile of VVV survey
- Short Name:
- J/A+A/571/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The intrinsically faint M dwarfs are the most numerous stars in the Galaxy, have main-sequence lifetimes longer than the Hubble time, and host some of the most interesting planetary systems known to date. Their identification and classification throughout the Galaxy is crucial to unraveling the processes involved in the formation of planets, stars, and the Milky Way. The ESO Public Survey VVV is a deep near-IR survey mapping the Galactic bulge and southern plane. The VVV b201 tile, located in the border area of the bulge, was specifically selected for the characterisation of M dwarfs. We used VISTA photometry to identify M dwarfs in the VVV b201 tile, to estimate their subtypes, and to search for transit-like light curves from the first 26 epochs of the survey.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/2618
- Title:
- M-dwarfs in Multiples (MinMs) survey. I.
- Short Name:
- J/MNRAS/449/2618
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a large-scale, volume-limited companion survey of 245 late-K to mid-M (K7-M6) dwarfs within 15pc. Infrared adaptive optics (AO) data were analysed from the Very Large Telescope, Subaru Telescope, Canada-France-Hawaii Telescope, and MMT Observatory to detect close companions to the sample from ~1 to 100AU, while digitized wide-field archival plates were searched for wide companions from ~100 to 10000AU. With sensitivity to the bottom of the main sequence over a separation range of 3 to 10000AU, multiple AO and wide-field epochs allow us to confirm candidates with common proper motions, minimize background contamination, and enable a measurement of comprehensive binary statistics. We detected 65 comoving stellar companions and find a companion star fraction of 23.5+/-3.2 percent over the 3 au to 10000AU separation range. The companion separation distribution is observed to rise to a higher frequency at smaller separations, peaking at closer separations than measured for more massive primaries. The mass ratio distribution across the q=0.2-1.0 range is flat, similar to that of multiple systems with solar-type primaries. The characterization of binary and multiple star frequency for low-mass field stars can provide crucial comparisons with star-forming environments and hold implications for the frequency and evolutionary histories of their associated discs and planets.
- ID:
- ivo://CDS.VizieR/J/AJ/154/124
- Title:
- M dwarfs-long-term photometric variability
- Short Name:
- J/AJ/154/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report findings from a long-term photometric variability study of M dwarfs carried out at the SMARTS 0.9 m telescope at the Cerro Tololo Inter-American Observatory. As part of a multi-faceted effort to investigate the range of luminosities of M dwarfs of a given color on the Hertzsprung-Russell Diagram, 76 M dwarfs have been observed for 3-17 years in the Johnson-Kron-Cousins V band. We find that stars elevated above the center of the main sequence distribution tend to have higher levels of variability, likely caused by magnetic activity, than their fainter counterparts below the center. This study provides insight into how the long-term magnetic activity of these stars may be affecting their sizes, luminosities, and thus positions on the H-R Diagram.
- ID:
- ivo://CDS.VizieR/J/A+A/505/859
- Title:
- M dwarfs radial velocities
- Short Name:
- J/A+A/505/859
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radial velocity (RV) measurements of our sample of 40 M dwarfs from our planet search programme with VLT+UVES begun in 2000. Although with our RV precision down to 2-2.5m/s and timebase line of up to 7 years we are capable of finding planets of few Earth masses in the close-in habitable zones of M dwarfs, there is no detection of a planetary companion. To demonstrate this we present mass detection limits allowing us to exclude Jupiter mass planets up to 1AU for most of our sample stars. We identified 6 M dwarfs that host a brown dwarf or low mass stellar companion. With the exception of these, all other sample stars show low RV variability with an rms <20m/s. Some high proper motion stars exhibit a linear RV trend consistent with their secular acceleration. Furthermore, we examine our data sets for a possible correlation between RVs and stellar activity as seen in variations of the Halpha line strength. For Barnard's star we found a significant anticorrelation, but most of the sample stars do not show such a correlation.
- ID:
- ivo://CDS.VizieR/J/AJ/155/225
- Title:
- M dwarf stars rotational broadening measurements
- Short Name:
- J/AJ/155/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Main-sequence, fully convective M dwarfs in eclipsing binaries are observed to be larger than stellar evolutionary models predict by as much as 10%-15%. A proposed explanation for this discrepancy involves effects from strong magnetic fields, induced by rapid rotation via the dynamo process. Although, a handful of single, slowly rotating M dwarfs with radius measurements from interferometry also appear to be larger than models predict, suggesting that rotation or binarity specifically may not be the sole cause of the discrepancy. We test whether single, rapidly rotating, fully convective stars are also larger than expected by measuring their Rsini distribution. We combine photometric rotation periods from the literature with rotational broadening (vsini) measurements reported in this work for a sample of 88 rapidly rotating M dwarf stars. Using a Bayesian framework, we find that stellar evolutionary models underestimate the radii by 10%-15%_-2.5_^+3^, but that at higher masses (0.18<M<0.4 M_Sun_), the discrepancy is only about 6% and comparable to results from interferometry and eclipsing binaries. At the lowest masses (0.08<M<0.18 M_Sun_), we find that the discrepancy between observations and theory is 13%-18%, and we argue that the discrepancy is unlikely to be due to effects from age. Furthermore, we find no statistically significant radius discrepancy between our sample and the handful of M dwarfs with interferometric radii. We conclude that neither rotation nor binarity are responsible for the inflated radii of fully convective M dwarfs, and that all fully convective M dwarfs are larger than models predict.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/146
- Title:
- M dwarfs with IR excess
- Short Name:
- J/ApJ/794/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70841) that show IR flux greater than the typical dM photosphere levels at 12 and/or 22{mu}m, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined spectral energy distributions. Our observed IR fluxes are greater than levels expected from ultracool companions (>3{sigma}). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is <0.1%. Using SDSS spectra we measure surface gravity-dependent features (K, Na, and CaH 3) and find <15% of our sample indicates low surface gravities. Examining tracers of youth (H{alpha}, UV fluxes, and Li absorption), we find <3% of our sample appear young, indicating we are observing a population of field stars >~1Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z|~700pc and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include (1) collisions of planetary bodies, (2) tidal disruption of planetary bodies, or (3) failed planet formation.
- ID:
- ivo://CDS.VizieR/J/AJ/129/2428
- Title:
- M dwarf-white dwarf binary systems
- Short Name:
- J/AJ/129/2428
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. We present the measured radial velocities and complete space motions for 161 white dwarf stars in wide binaries.
