- ID:
- ivo://CDS.VizieR/J/MNRAS/457/2192
- Title:
- NCJM catalog of M dwarfs
- Short Name:
- J/MNRAS/457/2192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop a method to identify the spectroscopic signature of unresolved L-dwarf ultracool companions, which compares the spectra of candidates and their associated control stars using spectral ratio differences and residual spectra. We present SpeX prism-mode spectra (0.7-2.5 micron) for a pilot sample of one hundred and eleven mid M dwarfs, including twenty-eight which were previously identified as candidates for unresolved ultracool companionship (a sub-sample from Cook et al. 2016; paper 1) and eighty-three single M dwarfs which were optically colour-similar to these candidates (which we use as `control stars'). We identify four candidates with evidence for near-infrared excess. One of these (WISE J100202.50+074136.3) shows strong evidence for an unresolved L dwarf companion in both its spectral ratio difference and its residual spectra, two most likely have a different source for the near-infrared excess, and the other may be due to spectral noise. We also establish expectations for a null result (i.e. by searching for companionship signatures around the M dwarf control stars), as well as determining the expected outcome for ubiquitous companionship (as a means of comparison with our actual results), using artificially generated unresolved M+L dwarf spectra. The results of these analyses are compared to those for the candidate sample, and reasonable consistency is found. With a full follow-up program of our candidates sample from paper 1, we might expect to confirm up to 40 such companions in the future, adding extensively to the known desert population of M3-M5 dwarfs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/585/A12
- Title:
- Nearby early-type stars spectroscopic survey
- Short Name:
- J/A+A/585/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a high signal-to-noise spectroscopic survey of 670 nearby early-type stars, to map Diffuse Interstellar Band (DIB) absorption in and around the Local Bubble. The project started with a Southern hemisphere survey conducted at the European Southern Observatory's New Technology Telescope and has since been extended to an all-sky survey using the Isaac Newton Telescope. In this first paper in the series, we introduce the overall project and present the results from the Southern hemisphere survey. We make available a catalogue of equivalent-width measurements of the DIBs at 5780, 5797, 5850, 6196, 6203, 6270, 6283 & 6614{AA}, the interstellar NaI D lines at 5890 & 5896{AA}, and the stellar HeI line at 5876{AA}. We find that the 5780{AA} DIB is relatively strong throughout, as compared to the 5797{AA} DIB, but especially within the Local Bubble and at the interface with more neutral medium. The 6203{AA} DIB shows a similar behaviour, but with respect to the 6196{AA} DIB. Some nearby stars show surprisingly strong DIBs whereas some distant stars show very weak DIBs, indicating small-scale structure within as well as outside the Local Bubble. The sight-lines with non-detections trace the extent of the Local Bubble especially clearly, and show it opening out into the Halo. The Local Bubble has a wall which is in contact with hot gas and/or a harsh interstellar radiation field. That wall is perforated though, causing leakage of radiation and possibly hot gas. On the other hand, compact self-shielded cloudlets are present much closer to the Sun, probably within the Local Bubble itself. As for the carriers of the DIBs, our observations confirm the notion that these are large molecules, whose differences in behaviour are mainly governed by their differing resilience and/or electrical charge, with more subtle differences possibly related to varying excitation.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A79
- Title:
- Nearby FGK stars chromospheric activity
- Short Name:
- J/A+A/520/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. Moreover, spots clearly affect the spectral line profiles. Such perturbations will in turn affect the line centroids creating a radial velocity jitter that might "contaminate" the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star. The purpose of this paper is to obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d<25pc) cool (spectral types F to K) stars, in order to estimate the activity-related jitter that should be expected for them. As a complementary objective, in this paper we aim to obtain relationships between fluxes in different activity indicator lines, which will permit a transformation of traditional activity indicators, i.e, CaII H & K lines, to other which hold noteworthy advantages. We used high resolution (~50000) echelle optical spectra. Standard data reduction was performed using the IRAF echelle package. To reveal the chromospheric emission of the stars in the sample we used the spectral subtraction technique. We measured equivalent widths of the chromospheric emission lines in the subtracted spectrum and transformed them into fluxes by applying empirical equivalent width-flux relationships. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity (RV) jitter we used empirical relationships between this and the R'HK index. We have measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected rotational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we have used the measured chromospheric activity to estimate the expected RV jitter for the active stars in the sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/173
- Title:
- Nearby low-mass stars proper motions
- Short Name:
- J/ApJ/862/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper uses the multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE) to demonstrate a method to measure proper motions and trigonometric parallaxes with precisions of ~4mas/yr and ~7mas, respectively, for low-mass stars and brown dwarfs. This method relies on WISE single exposures (Level 1b frames) and a Markov Chain Monte Carlo method. The limitations of Gaia in observing very low-mass stars and brown dwarfs are discussed, and it is shown that WISE will be able to measure astrometry past the 95% completeness limit and magnitude limit of Gaia (L, T, and Y dwarfs fainter than G~=19 and G=21, respectively). This method is applied to WISE data of 20 nearby (<=17pc) dwarfs with spectral types between M6-Y2 and previously measured trigonometric parallaxes. Also provided are WISE astrometric measurements for 23 additional low-mass dwarfs with spectral types between M6-T7 and estimated photometric distances <17pc. Only nine of these objects contain parallaxes within Gaia Data Release 2.
- ID:
- ivo://CDS.VizieR/J/AJ/126/2449
- Title:
- Nearby ultracool dwarfs in galactic plane
- Short Name:
- J/AJ/126/2449
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Surveys for nearby low-luminosity dwarfs tend to avoid the crowded regions of the Galactic plane. We have devised near-infrared color-magnitude and color-color selection criteria designed to identify late-type M and early-type L dwarfs within 12pc of the Sun. We use those criteria to search for candidates within the regions of the Galactic plane (|b|<10{deg}) covered by the Second Incremental Data Release from the Two Micron All Sky Survey (<II/241>). Detailed inspection of the available photographic images of the resulting 1299 candidates confirms only two as ultracool dwarfs. Both are known proper-motion stars, identified in the recent survey by Lepine et al. (2003, Cat. <J/AJ/125/1598>). Despite the low numbers, the inferred surface density is consistent with comparable surveys at higher latitudes. We discuss the implications for the luminosity function and consider means of improving the efficiency and scope of photometric surveys in the plane.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/173
- Title:
- Nearby young stars in Northern hemisphere
- Short Name:
- J/MNRAS/452/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a kinematically-unbiased search to identify young, nearby low-mass members of kinematic moving groups (MGs). Objects with both rotation periods shorter than 5 days in the SuperWASP All-Sky Survey and X-ray counterparts in the ROSAT All-Sky Survey were chosen to create a catalog of several thousand rapidly-rotating, X-ray active FGK stars. These objects are expected to be either genuinely young (<200Myr) single stars or tidally-locked spectroscopic binaries. We obtained optical spectra for a sub-sample of 146 stars to determine their ages and kinematics, and in some cases repeat radial velocity (RV) measurements were used to identify binarity. Twenty-six stars are found to have lithium abundances consistent with an age of 200Myr or younger and show no evidence for binarity, and in most cases measurements of Halpha and v sin i support their youthful status. Based on their youth, their radial velocities and estimates of their 3-dimensional kinematics, we find 11 objects that may be members of known MGs, 8 that do not appear associated with any young MG and a further 7 that are close to the kinematics of the recently proposed "Octans-Near" MG, and may be the first members of this MG found in the northern hemisphere. The initial search mechanism was ~18 per cent efficient at identifying likely-single stars younger than 200Myr, of which 80 per cent were early-K spectral types. A more complete survey may result in the detection of new nearby MGs, particularly in the comparatively little sampled northern hemisphere.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A127
- Title:
- Near-IR integral field spectra of 15 M-L dwarfs
- Short Name:
- J/A+A/562/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At young ages, low surface gravity affects the atmospheric properties of ultracool dwarfs. The impact on medium-resolution near-infrared (NIR) spectra has only been slightly investigated at the M-L transition sofar. We present a library of near-infrared (1.1-2.45um) medium-resolution (R~1500-2000) integral field spectra of 15 young M6-L0 dwarfs. We aim at deriving updated NIR spectral type, luminosity and physical parameters (Teff, logg, M, L/L_{sun}_) of each source. This work also aims at testing the latest generation of BT-SETTL atmospheric models. We estimated spectral types using spectral indices and spectra of reference young objects classified in the optical. We used the 2010 and 2012 releases of the BT-SETTL synthetic spectral grid and cross-checked the results with the DRIFT-PHOENIX models to derive the atmospheric properties of the sources.
- ID:
- ivo://CDS.VizieR/J/ApJS/151/387
- Title:
- Near-IR spectral library of late-type stars
- Short Name:
- J/ApJS/151/387
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an empirical infrared spectral library of medium-resolution (R~2000-3000) H (1.6{mu}m) and K (2.2{mu}m) band spectra of 218 red stars, spanning a range of [Fe/H] from ~-2.2 to ~+0.3. The sample includes Galactic disk stars, bulge stars from Baade's window, and red giants from Galactic globular clusters. We report the values of 19 indices covering 12 spectral features measured from the spectra in the library. Finally, we derive calibrations to estimate the effective temperature, and diagnostic relationships to determine the luminosity classes of individual stars from near-infrared spectra. This paper is part of a larger effort aimed at building a near-IR spectral library to be incorporated in population synthesis models, as well as at testing synthetic stellar spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/479/131
- Title:
- Near-IR spectra of inner red giants
- Short Name:
- J/A+A/479/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The existence in the Milky Way of either a long thin bar with a half length of 4.5kpc and a position angle of around 45{deg} with respect to the Sun-Galactic centre line or a bulge+bar complex, thicker and shorter, with a smaller tilt respect to the Sun-GC line, has been a matter of discussion in recent decades. In this paper, we present low resolution (R=500) near-infrared spectra for selected and serendipitous sources in six inner in-plane Galactic fields at l=7{deg}, 12{deg}, 15{deg}, 20{deg}, 26{deg} and 27{deg}, with the aim of analysing the stellar content present in those fields.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/112
- Title:
- NEOWISE/AllWISE high proper motion objects
- Short Name:
- J/ApJ/817/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Wide-field Infrared Survey Explorer (WISE) was reactivated in 2013 December (NEOWISE) to search for potentially hazardous near-Earth objects. We have conducted a survey using the first sky pass of NEOWISE data and the AllWISE catalog to identify nearby stars and brown dwarfs with large proper motions ({mu}_total_>~250mas/yr). A total of 20548 high proper motion objects were identified, 1006 of which are new discoveries. This survey has uncovered a significantly larger sample of fainter objects (W2>~13mag) than the previous WISE motion surveys of Luhman (2014, J/ApJ/781/4) and Kirkpatrick et al. (2014, J/ApJ/783/122). Many of these objects are predicted to be new L and T dwarfs based on near- and mid-infrared colors. Using estimated spectral types along with distance estimates, we have identified several objects that likely belong to the nearby solar neighborhood (d<25pc). We have followed up 19 of these new discoveries with near-infrared or optical spectroscopy, focusing on potentially nearby objects, objects with the latest predicted spectral types, and potential late-type subdwarfs. This subset includes six M dwarfs, five of which are likely subdwarfs, as well as eight L dwarfs and five T dwarfs, many of which have blue near-infrared colors. As an additional supplement, we provide 2MASS and AllWISE positions and photometry for every object found in our search, as well as 2MASS/AllWISE calculated proper motions.
