scholarly journals The substructure of the Perseus star-forming region: a survey with Gaia DR2

2021 ◽  
Vol 503 (3) ◽  
pp. 3232-3242
Author(s):  
Tatiana Pavlidou ◽  
Aleks Scholz ◽  
Paula S Teixeira
Keyword(s):  
Proper Motion ◽  
Motion Parallax ◽  
Young Stars ◽  
Galactic Latitude ◽  
Proper Motions ◽  
Kinematic Data ◽  
Star Forming ◽  
Moving Groups ◽  
Cold Dust ◽  
Gaia Dr2

ABSTRACT We use photometric and kinematic data from Gaia DR2 to explore the structure of the star-forming region associated with the molecular cloud of Perseus. Apart from the two well-known clusters, IC 348 and NGC 1333, we present five new clustered groups of young stars, which contain between 30 and 300 members, named Autochthe, Alcaeus, Heleus, Electryon, and Mestor. We demonstrate that these are co-moving groups of young stars, based on how the candidate members are distributed in position, proper motion, parallax, and colour–magnitude space. By comparing their colour–magnitude diagrams to isochrones, we show that they have ages between 1 and 5 Myr. Using 2MASS and WISE colours, we find that the fraction of stars with discs in each group ranges from 10 to ∼50 per cent. The youngest of the new groups is also associated with a reservoir of cold dust, according to the Planck map at 353 GHz. We compare the ages and proper motions of the five new groups to those of IC 348 and NGC 1333. Autochthe is clearly linked with NGC 1333 and may have formed in the same star formation event. The seven groups separate roughly into two sets that share proper motion, parallax, and age: Heleus, Electryon, and Mestor as the older set, and NGC 1333 and Autochthe as the younger set. Alcaeus is kinematically related to the younger set, but at a more advanced age, while the properties of IC 348 overlap with both sets. All older groups in this star-forming region are located at higher galactic latitude.

scholarly journals New ultracool dwarf neighbours within 20 pc from Gaia DR2

2020 ◽  
Vol 637 ◽  
pp. A45
Author(s):  
R.-D. Scholz
Keyword(s):  
Proper Motion ◽  
Visual Inspection ◽  
Near Infrared ◽  
Galactic Plane ◽  
Proper Motions ◽  
Magnitude Diagram ◽  
Motion Measurements ◽  
Moving Groups ◽  
Absolute Magnitudes ◽  
Gaia Dr2

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. Because the expected numbers based on 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) has been verified and completed with Gaia DR2. We here confirm 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 MG versus 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 MG >  14 mag (used to define UCDs in this study) for the correctness of their Gaia DR2 proper motions by 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 that are not mentioned in three previous studies using Gaia DR2. They have relatively small proper motions and low 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.

scholarly journals New member candidates of Upper Scorpius from Gaia DR1

2018 ◽  
Vol 618 ◽  
pp. A12 ◽  
Author(s):  
S. Wilkinson ◽  
B. Merín ◽  
P. Riviere-Marichalar
Keyword(s):  
Proper Motion ◽  
Clustering Algorithm ◽  
Proper Motions ◽  
Established Method ◽  
Kinematic Data ◽  
Star Forming ◽  
Density Based Clustering ◽  
Member Selection ◽  
Bona Fide ◽  
And Performance

Context. Selecting a cluster in proper motion space is an established method for identifying members of a star-forming region. The first data release from Gaia (DR1) provides an extremely large and precise stellar catalogue, which when combined with the Tycho-2 catalogue gives the 2.5 million parallaxes and proper motions contained within the Tycho-Gaia Astrometric Solution (TGAS). Aims. We aim to identify new member candidates of the nearby Upper Scorpius subgroup of the Scorpius-Centaurus Complex within the TGAS catalogue. In doing so, we also aim to validate the use of a density-based clustering algorithm (DBSCAN) on spatial and kinematic data as a robust member selection method. Methods. We constructed a method for member selection using a density-based clustering algorithm (DBSCAN) applied over proper motion and distance. We then applied this method to Upper Scorpius and evaluated the results and performance of the method. Results. We identified 167 member candidates of Upper Scorpius, of which 78 are new, distributed within a 10° radius from its core. These member candidates have a mean distance of 145.6 ± 7.5 pc and a mean proper motion of (−11.4, −23.5) ± (0.7, 0.4) mas yr−1. These values are consistent with measured distances and proper motions of previously identified bona fide members of the Upper Scorpius association.

scholarly journals Gaia DR2 reveals a very massive runaway star ejected from R136

2018 ◽  
Vol 619 ◽  
pp. A78 ◽  
Author(s):  
D. J. Lennon ◽  
C. J. Evans ◽  
R. P. van der Marel ◽  
J. Anderson ◽  
I. Platais ◽  
...  
Keyword(s):  
Lower Limit ◽  
Proper Motion ◽  
Evolutionary History ◽  
Massive Star ◽  
Position Angle ◽  
Proper Motions ◽  
Central Cluster ◽  
Dynamical Constraints ◽  
Runaway Stars ◽  
Gaia Dr2

A previous spectroscopic study identified the very massive O2 III star VFTS 16 in the Tarantula Nebula as a runaway star based on its peculiar line-of-sight velocity. We use the Gaia DR2 catalog to measure the relative proper motion of VFTS 16 and nearby bright stars to test if this star might have been ejected from the central cluster, R136, via dynamical ejection. We find that the position angle and magnitude of the relative proper motion (0.338±0.046 mas yr−1, or approximately 80±11 km s−1) of VFTS 16 are consistent with ejection from R136 approximately 1.5±0.2 Myr ago, very soon after the cluster was formed. There is some tension with the presumed age of VFTS 16 that, from published stellar parameters, cannot be greater than 0.9+0.3−0.2 Myr. Older ages for this star would appear to be prohibited due to the absence of He I lines in its optical spectrum, since this sets a firm lower limit on its effective temperature. The dynamical constraints may imply an unusual evolutionary history for this object, perhaps indicating it is a merger product. Gaia DR2 also confirms that another very massive star in the Tarantula Nebula, VFTS 72 (alias BI 253; O2 III-V(n)((f*)), is also a runaway on the basis of its proper motion as measured by Gaia. While its tangential proper motion (0.392±0.062 mas yr−1 or 93±15 km s−1) would be consistent with dynamical ejection from R136 approximately 1 Myr ago, its position angle is discrepant with this direction at the 2σ level. From their Gaia DR2 proper motions we conclude that the two ∼100 M⊙ O2 stars, VFTS 16 and VFTS 72, are fast runaway stars, with space velocities of around 100 km s−1 relative to R136 and the local massive star population. The dynamics of VFTS 16 are consistent with it having been ejected from R136, and this star therefore sets a robust lower limit on the age of the central cluster of ∼1.3 Myr.

scholarly journals Prediction of astrometric microlensing events from Gaia DR2 proper motions

2018 ◽  
Vol 620 ◽  
pp. A175 ◽  
Author(s):  
J. Klüter ◽  
U. Bastian ◽  
M. Demleitner ◽  
J. Wambsganss
Keyword(s):  
Proper Motion ◽  
Proper Motions ◽  
Stellar Objects ◽  
Gravitational Microlensing ◽  
Data Release ◽  
The Future ◽  
Nested Intervals ◽  
Excellent Tool ◽  
Gaia Dr2

Context. Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of the lens and the unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Aims. Making use of the recently published Gaia Data Release 2 (DR2) catalogue, we want to predict astrometric microlensing events caused by foreground stars with high proper motion passing a background source in the coming decades. Results. We selected roughly 148 000 high-proper-motion stars from Gaia DR2 with μtot > 150 mas yr−1 as potential lenses. We then searched for background sources close to their paths. Using the astrometric parameters of Gaia DR2, we calculated the future positions of source and lens. With a nested-intervals algorithm we determined the date and separation of the closest approach. Using Gaia DR2 photometry we determined an approximate mass of the lens, which we used to calculate the expected microlensing effects. Conclusions. We predict 3914 microlensing events caused by 2875 different lenses between 2010 and 2065, with expected shifts larger than 0.1 mas between the lensed and unlensed positions of the source. Of those, 513 events are expected to happen between 2014.5 and 2026.5 and might be measured by Gaia. For 127 events we also expect a magnification between 1 mmag and 3 mag.

scholarly journals Determination of kinematic distances of pre-main-sequence stars in star-forming regions

2009 ◽  
Vol 5 (S266) ◽  
pp. 395-398
Author(s):  
Phillip A. B. Galli ◽  
Ramachrisna Teixeira ◽  
Christine Ducourant ◽  
Claude Bertout
Keyword(s):  
Main Sequence ◽  
Young Stars ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Know How ◽  
Star Forming Regions ◽  
Moving Groups ◽  
Kinematic Properties

AbstractMany studies of star-forming regions have been carried out since the discovery of compact Hii regions in the late 1960s. The kinematic properties of young stars in the nearest regions with ongoing and recent star formation provide essential tests of their formation mechanisms. The detection of coeval moving groups allows determination of individual distances through the convergent-point method. As a result, the main physical properties of these stars and their early evolutionary stages can be determined if we know how distant they are.

scholarly journals Proper motions of water masers: W 51 North, Main, and South

2002 ◽  
Vol 206 ◽  
pp. 88-91 ◽  
Author(s):  
Hiroshi Imai ◽  
Tetsuo Sasao ◽  
Osamu Kameya ◽  
Teruhiko Watanabe ◽  
Toshihiro Omodaka ◽  
...  
Keyword(s):  
Proper Motion ◽  
Massive Star ◽  
Model Fitting ◽  
Proper Motions ◽  
Star Forming ◽  
Motion Measurements ◽  
Water Masers ◽  
Reference Feature

We describe the proper motion measurements of water masers in the massive-star forming region W 51A and the analysis of the 3-D kinematics in three maser clusters of W 51A. We found a systematic expanding motion in one of the clusters named W 51 North, while no systematic motion was detected in other two clusters named W 51 Main and South. The 3-D motions of the clusters relative to the position reference feature in W 51 North indicate a separating motion between the W 51 North and the W 51 Main/South clusters. We estimated the distance to W 51 North as to be 6.7±2.1 kpc on basis of the statistical parallax and the model fitting methods.

scholarly journals A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes

2018 ◽  
Vol 616 ◽  
pp. L15 ◽  
Author(s):  
Y. Xu ◽  
S. B. Bian ◽  
M. J. Reid ◽  
J. J. Li ◽  
B. Zhang ◽  
...  
Keyword(s):  
Spiral Structure ◽  
Young Stars ◽  
Solar Neighborhood ◽  
Proper Motions ◽  
Data Set ◽  
Ob Stars ◽  
Three Samples ◽  
Significant Distance ◽  
Gaia Dr2 ◽  
Spiral Arm

Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.

scholarly journals The Distance to the Center of the Galaxy

1987 ◽  
Vol 115 ◽  
pp. 554-555 ◽  
Author(s):  
M. J. Reid ◽  
M. H. Schneps ◽  
J. M. Moran ◽  
C. R. Gwinn ◽  
R. Genzel ◽  
...  
Keyword(s):  
Proper Motion ◽  
Radial Component ◽  
Proper Motions ◽  
Star Forming ◽  
The Galaxy

The distance to a star forming region can be determined by measuring the proper motions within H2O maser clusters. If the motions of the maser spots are random, the distance can be determined by applying the technique known as statistical parallax. Alternatively, if organized motions are evident in the proper motions, one can model the source to estimate its the distance. Both methods rely on a comparison of the radial component of the motion (in km/s) and the proper motion on the plane of the sky (in milli-arcseconds/year).

scholarly journals The brown dwarf population in the star-forming region NGC 2264

2020 ◽  
Vol 499 (2) ◽  
pp. 2292-2302
Author(s):  
Samuel Pearson ◽  
Aleks Scholz ◽  
Paula S Teixeira ◽  
Koraljka Mužić ◽  
Jochen Eislöffel
Keyword(s):  
Proper Motion ◽  
Near Infrared ◽  
Mass Range ◽  
Young Stars ◽  
Brown Dwarf ◽  
Star Forming ◽  
Rotation Periods ◽  
Colour Excess ◽  
High Level

ABSTRACT The brown dwarf population in the canonical star-forming region NGC 2264 is so far poorly explored. We present a deep, multiwavelength, multiepoch survey of the star-forming cluster NGC 2264, aimed to identify young brown dwarf candidates in this region. Using criteria including optical/near-infrared (IR) colours, variability, Spitzer mid-IR colour excess, extinction, and Gaia parallax and proper motion (in order of relevance), we select 902 faint red sources with indicators of youth. Within this sample, we identify 429 brown dwarf candidates based on their IR colours. The brown dwarf candidates are estimated to span a mass range from 0.01 to 0.08 M⊙. We find rotation periods for 44 sources, 15 of which are brown dwarf candidates, ranging from 3.6 h to 6.5 d. A subset of 38 brown dwarf candidates show high-level irregular variability indicative of ongoing disc accretion, similar to the behaviour of young stars.

scholarly journals A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

2018 ◽  
Vol 482 (3) ◽  
pp. 3023-3031 ◽  
Author(s):  
L Petrov ◽  
Y Y Kovalev ◽  
A V Plavin
Keyword(s):  
Proper Motion ◽  
Rayleigh Distribution ◽  
Degree Of Freedom ◽  
Proper Motions ◽  
Position Uncertainty ◽  
Long Baseline ◽  
Median Position ◽  
Chi Squared ◽  
Best Fit ◽  
Gaia Dr2

ABSTRACT We have analysed the differences in positions of 9081 matched sources between the Gaia Data Release 2 (DR2) and very long baseline interferometry (VLBI) catalogues. The median position uncertainty of matched sources in the VLBI catalogue is a factor of two larger than the median position uncertainty in Gaia DR2. There are 9 per cent matched sources with statistically significant offsets between both catalogues. We found that the reported positional errors should be rescaled by a factor of 1.3 for VLBI and 1.06 for Gaia and, in addition, the Gaia errors should be multiplied by the square root of chi squared per degree of freedom in order to best fit the normalized position differences to the Rayleigh distribution. We have established that the major contributor to statistically significant position offsets is the presence of optical jets. Among the sources for which the jet direction was determined, the position offsets are parallel to the jet directions for 62 per cent of the outliers. Among the matched sources with significant proper motion, the fraction of objects with proper motion directions parallel to jets is a factor of three greater than on average. Such sources have systematically higher chi squared per degree of freedom. We explain these proper motions as a manifestation of the source position jitter caused by flares, which we predicted earlier. Therefore, the assumption that quasars are fixed points, and thus that differential proper motions determined with respect to quasar photocentres can be regarded as absolute proper motions, should be treated with great caution.

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