New ultra-cool and brown dwarf candidates in <i>Gaia</i> DR2

Reylé, C.

doi:10.1051/0004-6361/201834082

Cited by 66 publications

(72 citation statements)

References 45 publications

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“…2). There was only one object in common with the above mentioned subsample of 134 ob- jects from Smart et al (2019), and the missing VVV J17134060-39521521 was found among those 25 objects from Reylé (2018). These 25 UCD candidates are systematically brighter in absolute magnitudes (13.7 mag< M G <17.4 mag, with a peak at M G ≈15 mag) than the 134 objects from Smart et al (2019) (14.5 mag< M G <21.7 mag, with a peak at M G ≈17 mag).…”

Section: Known Ucds and Wdsmentioning

confidence: 86%

“…The remaining two UCD candidate members of the Gaia DR2 20 pc sample from Smith et al (2018) are the L5 dwarf VVV J17264015-27380372 formerly discovered as VVV BD001 by Beamín et al (2013) and included in Smart et al (2019), and another mid-L dwarf candidate (with similar M G ≈16.7 mag and colour G−RP≈1.7 mag), VVV J17134060-39521521, that is missing in Smart et al (2019). Reylé (2018) searched for new UCD candidates in Gaia DR2 and found 14 915 objects, all with available G−RP colours, and provided spectral type estimates based on photometry. According to these estimates, given in the corresponding machinereadable table including only few of the original Gaia DR2 data (without errors), most of the candidates are late M dwarfs, whereas only 280 (<2%) are L dwarfs.…”

Section: Known Ucds and Wdsmentioning

confidence: 99%

“…In total, we identified 263 known UCDs from Bardalez Gagliuffi et al (2019), Smart et al (2019), and Reylé (2018) in the Gaia DR2 20 pc sample. Out of these 263 objects, 14 lack the BP−RP and G−RP colour measurements and belong to subsample E. The other 249 known UCDs are overplotted in Fig.…”

Section: Known Ucds and Wdsmentioning

confidence: 99%

“…To estimate mean spectral types, we applied four spectral type-absolute magnitude (M G , M J , M H , and M K s ) and three spectral type-colour (G − RP, G − J, and J − K s ) relations as given in Reylé (2018, their Table 1). For 27 out of 31 entries in Table1, and five out of 19 entries in Table 2, the relation between spectral type and G − J colour given by Reylé (2018) was not used as it was only valid for M9-T6 dwarfs. For the objects with partly lacking photometric measurements, the spectral types were estimated based on fewer data and are therefore less reliable.…”

Section: Photometric Classification Of New Ucdsmentioning

confidence: 99%

“…Parallaxes from the literature (T = trigonometric, P = photometric, all rounded to 1 mas) and spectral types from SIMBAD are also given, if available. Photometric spectral types were estimated using the relationships between spectral types and absolute magnitudes and colours given by Reylé (2018) using all available data, except for (a) (G − J not used) . Spectral type uncertainties represent standard deviations of the values determined from different relations for a given object.…”

Section: Photometric Classification Of New Ucdsmentioning

confidence: 99%

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New ultracool dwarf neighbours within 20 pc fromGaiaDR2

Scholz

2020

A&A

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Aims. The Gaia data release 2 (DR2) contains >6000 objects with parallaxes (Plx + 3 × e_Plx) > 50 mas placing them within 20 pc from the Sun. Since the expected numbers extrapolating the well-known 10 pc census are much lower, nearby Gaia stars need a quality assessment. The 20 pc sample of white dwarfs (WDs) had already been verified and completed with Gaia DR2. We aimed to check and complete the 20 pc sample of ultracool dwarfs (UCDs) with spectral types M7 and given Gaia DR2 parallaxes. Methods. Dividing the Gaia DR2 20 pc sample into subsamples of various astrometric and photometric quality, we studied their distribution on the sky, in the M G vs. G−RP colour-magnitude diagram (CMD), and as a function of G magnitude and total proper motion. After excluding 139 known WDs and 263 known UCDs from the CMD, we checked all remaining ≈3500 candidates with M G > 14 mag (used to define UCDs in this study) for the correctness of their Gaia DR2 proper motions via visual inspection of finder charts, comparison with proper motion catalogues, and comparison with our own proper motion measurements. For confirmed UCD candidates we estimated spectral types photometrically using Gaia and near-infrared absolute magnitudes and colours. Results. We failed to confirm new WDs, but found 50 new UCD candidates not mentioned in three previous studies using Gaia DR2. They have relatively small proper motions and tangential velocities and are concentrated towards the Galactic plane. Half of them have spectral types in SIMBAD and/or previous non-Gaia distance estimates that placed them already within 20 pc. For 20 of the 50 objects, we estimated photometric spectral types of M6-M6.5, slightly below the classical UCD spectral type limit. However, seven L4.5-L6.5, four L0-L1, five M8.5-M9.5, and three M7-M8 dwarfs can be considered as completely new UCDs discoveries within 20 pc based on Gaia DR2. Four M6.5 and two L4.5 dwarfs have high membership probabilities (64%-99%) in the ARGUS, AB Doradus, or Carina Near young moving groups.

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Section: Known Ucds and Wdsmentioning

confidence: 86%

Section: Known Ucds and Wdsmentioning

confidence: 99%

Section: Known Ucds and Wdsmentioning

confidence: 99%

Section: Photometric Classification Of New Ucdsmentioning

confidence: 99%

Section: Photometric Classification Of New Ucdsmentioning

confidence: 99%

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New ultracool dwarf neighbours within 20 pc fromGaiaDR2

Scholz

2020

A&A

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Gaia-predicted brown dwarf detection rates around FGK stars in astrometry, radial velocity, and photometric transits

Holl

Perryman

Lindegren

et al. 2022

A&A

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Context. After more than two decades of relevant radial velocity surveys, the current sample of known brown dwarfs (BDs) around FGK stars is only of the order of 100, limiting our understanding of their occurrence rate, properties, and formation. The ongoing ESA mission Gaia has already collected more than its nominal 5 years of mission data, and is expected to operate for up to 10 years in total. Its exquisite astrometric precision allows for the detection of (unseen) companions down to the Jupiter-mass level, allowing the efficient detection of large numbers of BDs. Additionally, its low-accuracy multi-epoch radial velocity measurements for GRVS < 12 can provide additional detections or constraints for the more massive BDs, while a further small sample will have detectable transits in Gaia photometry. Aims. Using detailed simulations, we provide an assessment of the number of BDs that could be discovered using Gaia astrometry, radial velocity, and photometric transits around main sequence (V) and subgiant (IV) FGK host stars for the nominal five-year and extended ten-year mission. Methods. Using a robust Δχ2 statistic we analyse the BD companion detectability from the Besançon Galaxy population synthesis model for G = 10.5 − 17.5 mag, complemented by Gaia DR2 data for G < 10.5, using the latest Gaia performance and scanning law, and literature-based BD-parameter distributions. Results. We report here only reliable detection numbers with Δχ2 > 50 for a five-year mission, and those in square brackets are for a ten-year mission. For astrometry alone, we expect 28 000–42 000 [45 000–55 000] detections out to several hundred parsecs [up to more than a kiloparsec]. The majority of these have G ∼ 14 − 15 [14 − 16] and periods of greater than 200 d, extending up to the longest simulated periods of 5 yr. Gaia radial velocity time-series for GRVS < 12 (G ≲ 12.7), should allow the detection of 830–1100 [1500–1900] BDs, most having orbital periods of < 10 days, and being amongst the most massive BDs (55 − 80MJ), though several tens will extend down to the ‘desert’ and lowest BD masses. Systems with at least three photometric transits with S/N > 3 are expected for 720–1100 [1400–2300] BDs, averaging at 4–5 [5–6] transits per source. The combination of astrometric and radial velocity detections should yield some 370–410 [870–950] detections. Perhaps 17–27 [35–56] BDs will have both transit and radial velocity detections, while both transits and astrometric detection will lead to a meagre 1–3 [4–6] detection(s). Conclusions. Though the above numbers are affected by ±50% uncertainty due to the uncertain occurrence rate and period distribution of BDs around FGK host stars, detections of BDs with Gaia will number in the tens of thousands, enlarging the current BD sample by at least two orders of magnitude, allowing us to investigate the BD fraction and orbital architectures as a function of host stellar parameters in greater detail than every before.

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SPECULOOS: Ultracool dwarf transit survey

Sebastian

Gillon

Ducrot

et al. 2021

A&A

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Context. One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to make it possible to carry out a thorough atmospheric characterisation with next-generation telescopes, such as the James Webb Space telescope (JWST) or Extremely Large Telescope (ELT). In this context, the TRAPPIST-1 planets form a unique benchmark system that has garnered the interest of a large scientific community. Aims. The SPECULOOS survey is an exoplanet transit survey targeting a volume-limited (40 pc) sample of ultracool dwarf stars (of spectral type M7 and later) that is based on a network of robotic 1 m telescopes especially designed for this survey. The strategy for brighter and earlier targets leverages the synergy with the ongoing TESS space-based exoplanet transit survey. Methods. We define the SPECULOOS target list as the sum of three non-overlapping sub-programmes incorporating the latest type objects (T eff 3000 K). Programme 1 features 365 dwarfs that are small and near enough to make it possible to detail atmospheric characterisation of an 'Earth-like' planet with the upcoming JWST. Programme 2 features 171 dwarfs of M5-type and later for which a significant detection of a planet similar to TRAPPIST-1b should be within reach of TESS. Programme 3 features 1121 dwarfs that are later than M6-type. These programmes form the basis of our statistical census of short-period planets around ultracool dwarf stars. Results. Our compound target list includes 1657 photometrically classified late-type dwarfs, with 260 of these targets classified, for the first time, as possible nearby ultracool dwarf stars. Our general observational strategy was to monitor each target between 100 and 200 hr with our telescope network, making efficient use of the synergy with TESS for our Programme 2 targets and a proportion of targets in our Programme 1. Conclusions. Based on Monte Carlo simulations, we expect to detect up to a few dozen temperate, rocky planets. We also expect a number of them to prove amenable for atmospheric characterisation with JWST and other future giant telescopes, which will substantially improve our understanding of the planetary population of the latest-type stars.

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New ultra-cool and brown dwarf candidates in Gaia DR2

Cited by 66 publications

References 45 publications

New ultracool dwarf neighbours within 20 pc fromGaiaDR2

New ultracool dwarf neighbours within 20 pc fromGaiaDR2

Gaia-predicted brown dwarf detection rates around FGK stars in astrometry, radial velocity, and photometric transits

SPECULOOS: Ultracool dwarf transit survey

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