scholarly journals Lessons from the curious case of the ‘fastest’ star in Gaia DR2

2019 ◽  
Vol 486 (2) ◽  
pp. 2618-2630 ◽  
Author(s):  
D Boubert ◽  
J Strader ◽  
D Aguado ◽  
G Seabroke ◽  
S E Koposov ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Radial Velocities ◽  
Galactic Dynamics ◽  
Intermediate Mass ◽  
Pm 2.5 ◽  
Gaia Dr2 ◽  
Radial Velocity Measurement ◽  
Selection Of

Abstract Gaia DR2 5932173855446728064 was recently proposed to be unbound from the Milky Way based on the $-614.3\pm 2.5\, \mathrm{km}\, \mathrm{s}^{-1}$ median radial velocity given in Gaia DR2. We obtained eight epochs of spectroscopic follow-up and find a very different median radial velocity of $-56.5 \pm 5.3\, \mathrm{km}\, \mathrm{s}^{-1}$. If this difference were to be explained by binarity, then the unseen companion would be an intermediate-mass black hole; we therefore argue that the Gaia DR2 radial velocity must be in error. We find it likely that the spectra obtained by Gaia were dominated by the light from a star $4.3\, \mathrm{arcsec}$ away, and that, due to the slitless, time delay integration nature of Gaia spectroscopy, this angular offset corresponded to a spurious $620\, \mathrm{km}\, \mathrm{s}^{-1}$ shift in the calcium triplet of the second star. We argue that such unanticipated alignments between stars may account for 105 of the 202 stars with radial velocities faster than $500\, \mathrm{km}\, \mathrm{s}^{-1}$ in Gaia DR2 and propose a quality cut to exclude stars that are susceptible. We propose further cuts to remove stars where the colour photometry is suspect and stars where the radial velocity measurement is based on fewer than four transits, and thus produce an unprecedentedly clean selection of Gaia radial velocities for use in studies of Galactic dynamics.

scholarly journals ARGOS – II. The Galactic bulge survey

2012 ◽  
Vol 428 (4) ◽  
pp. 3660-3670 ◽  
Author(s):  
K. Freeman ◽  
M. Ness ◽  
E. Wylie-de-Boer ◽  
E. Athanassoula ◽  
J. Bland-Hawthorn ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Radial Velocities ◽  
Galactic Centre ◽  
Red Giants ◽  
Formation Processes ◽  
Galactic Bulge ◽  
Milky Way Galaxy ◽  
Selection For ◽  
Metallicity Distribution

Abstract We describe the motivation, field locations and stellar selection for the Abundances and Radial velocity Galactic Origins Survey (ARGOS) spectroscopic survey of 28 000 stars in the bulge and inner disc of the Milky Way galaxy across latitudes of b = −5° to −10°. The primary goal of this survey is to constrain the formation processes of the bulge and establish whether it is predominantly a merger or instability remnant. From the spectra (R = 11 000), we have measured radial velocities and determined stellar parameters, including metallicities and [α/Fe] ratios. Distances were estimated from the derived stellar parameters and about 14 000 stars are red giants within 3.5 kpc of the Galactic Centre. In this paper, we present the observations and analysis methods. Subsequent papers (III and IV) will discuss the stellar metallicity distribution and kinematics of the Galactic bulge and inner disc, and the implications for the formation of the bulge.

scholarly journals RAVE-Gaia and the impact on Galactic archeology

2017 ◽  
Vol 12 (S330) ◽  
pp. 176-180
Author(s):  
Andrea Kunder
Keyword(s):  
Radial Velocity ◽  
Effective Temperature ◽  
Milky Way ◽  
Radial Velocities ◽  
Surface Gravity ◽  
Individual Stars ◽  
Dynamic Analyses ◽  
Data Release ◽  
The Impact ◽  
Temperature Surface

AbstractThe new data release (DR5) of the RAdial Velocity Experiment (RAVE) includes radial velocities of 520,781 spectra of 457,588 individual stars, of which 215,590 individual stars are released in the Tycho-Gaia astrometric solution (TGAS) in Gaia DR1. Therefore, RAVE contains the largest TGAS overlap of the recent and ongoing Milky Way spectroscopic surveys. Most of the RAVE stars also contain stellar parameters (effective temperature, surface gravity, overall metallicity), as well as individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni. Combining RAVE with TGAS brings the uncertainties in space velocities down by a factor of 2 for stars in the RAVE volume – 10 km s−1 uncertainties in space velocities are now able to be derived for the majority (70%) of the RAVE-TGAS sample, providing a powerful platform for chemo-dynamic analyses of the Milky Way. Here we discuss the RAVE-TGAS impact on Galactic archaeology as well as how the Gaia parallaxes can be used to break degeneracies within the RAVE spectral regime for an even better return in the derivation of stellar parameters and abundances.

scholarly journals An outline of the spiral structure of the Southern Milky Way

1964 ◽  
Vol 20 ◽  
pp. 147-155 ◽  
Author(s):  
B. J. Bok
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Spiral Structure ◽  
Star Clusters ◽  
Hii Regions ◽  
Radial Velocities ◽  
Optical Methods ◽  
Galactic Rotation ◽  
Interstellar Gas ◽  
Recent Origin

It has become clear in recent years that the spiral features of our Galaxy — like those of all galaxies — are of recent origin and are presumably short-lived phenomena. To trace them optically, we need to confine ourselves to concentrations in the interstellar gas and to stars and star groupings recently formed from these. We are hence limited primarily to OB associations and star clusters in which the earliest spectral types for the stars are not later than B2, preferably O5 to B1. It is most important that radial velocities be measured for a fair sampling of these stars, especially so for directions in which the radial velocity effects due to galactic rotation vary appreciably with distance. Radial velocities of the stars in question and those found from interstellar absorption lines are not only useful as indicators of distance, but they are very much needed for the identification of star groups and their associated HI clouds, found by 21-cm techniques. They assist also in the study of HII regions, which can now be located by either radio or optical methods.

scholarly journals Radial Velocity Observations of Binary Stars

1983 ◽  
Vol 62 ◽  
pp. 93-103
Author(s):  
C. D. Scarfe
Keyword(s):  
Radial Velocity ◽  
Binary Stars ◽  
Velocity Measurement ◽  
Cross Correlation ◽  
Radial Velocities ◽  
Measuring Instruments ◽  
Great Stability ◽  
Visual Binary Stars ◽  
Radial Velocity Measurement

AbstractThis review considers three main areas, leaving several others to be discussed in more detail in the contributed papers of this session.1.The need for spectrographs and measuring instruments of great stability for long-term projects such as radial velocity observations of visual binary stars.2.The use of cross-correlation devices, both analog (radial velocity scanners) and digital, for radial velocity measurement.3.The use of comparison spectra impressed directly onto the starlight and of polarisation instruments as means to very precise radial velocities.

scholarly journals Characterizing the Gaia radial velocity sample selection function in its native photometry

2020 ◽  
Vol 500 (1) ◽  
pp. 397-409
Author(s):  
Jan Rybizki ◽  
Hans-Walter Rix ◽  
Markus Demleitner ◽  
Coryn A L Bailer-Jones ◽  
William J Cooper
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Sample Selection ◽  
Small Scale ◽  
Apparent Magnitude ◽  
Selection Function ◽  
Source Density ◽  
Dimensional Phase Space ◽  
Data Release ◽  
Gaia Dr2

ABSTRACT The Gaia Data Release 2 (DR2) radial velocity sample (GDR2RVS), which provides six-dimensional phase-space information on 7.2 million stars, is of great value for inferring properties of the Milky Way. Yet a quantitative and accurate modelling of this sample is hindered without knowledge and inclusion of a well-characterized selection function. Here we derive the selection function through estimates of the internal completeness, i.e. the ratio of GDR2RVS sources compared to all Gaia DR2 sources (GDR2all). We show that this selection function or ‘completeness’ depends on basic observables, in particular the apparent magnitude GRVS and colour G − GRP, but also on the surrounding source density and on sky position, where the completeness exhibits distinct small-scale structure. We identify a region of magnitude and colour that has high completeness, providing an approximate but simple way of implementing the selection function. For a more rigorous and detailed description we provide python code to query our selection function, as well as tools and adql queries that produce custom selection functions with additional quality cuts.

scholarly journals Selection of most promising CoRoT candidates for radial-velocity follow-up

2009 ◽  
Vol 5 (H15) ◽  
pp. 690-690
Author(s):  
Ronaldo Da Silva ◽  
Adriana Silva-Valio
Keyword(s):  
Radial Velocity ◽  
Light Curves ◽  
Velocity Measurements ◽  
Preliminary Results ◽  
Exoplanetary Systems ◽  
Selection Of

AbstractWe used the method of Silva & Cruz (2006), which distinguishes between planetary and stellar companions by fitting transit light curves, to select the most promising CoRoT candidates to be monitored with radial-velocity measurements. Testing this method on the light curves of confirmed CoRoT exoplanetary systems shows that the estimated radius for such planets is smaller than 2 RJup, while for most of the light curves in which no planet has been detected, the secondary companion has an estimated radius larger than 2 RJup. We present preliminary results concerning other light curves for which no planet has been detected yet.

Bibliographic Catalogue

1984 ◽  
Vol 88 ◽  
pp. 351-351
Author(s):  
M. Barbier
Keyword(s):  
Radial Velocity ◽  
Data Center ◽  
Magnetic Tape ◽  
Radial Velocities

The increasing number of stellar radial velocity determinations and their publication in many journals necessitates the compilation of a continuously evolving bibliographic catalogue.The first stellar radial velocity catalogue was compiled by H. A. Abt and E. S. Biggs in 1972. It is complete up to 1970. At the Marseille Observatory, Mme. M. Petit and myself have undertaken a follow-up of this catalogue. Our presentation is nearly the same.We systematically examine all reviews of possible interest received in our library. Our bibliography does not include papers which do not publish new data on radial velocities. The first part of our catalogue, including about 5000 references between 1970 to 1975, was published on microfiche in 1979. This microfiche was prepared by the Strasbourg Stellar Data Center. The catalogue is available on magnetic tape from the Stellar Data Center. This first part was not complete and several corrections have been made.

scholarly journals A hyper-runaway white dwarf in Gaia DR2 as a Type Iax supernova primary remnant candidate

2019 ◽  
Vol 489 (1) ◽  
pp. 420-426 ◽  
Author(s):  
Nicholas J Ruffini ◽  
Andrew R Casey
Keyword(s):  
White Dwarf ◽  
High Velocity ◽  
White Dwarfs ◽  
Milky Way ◽  
Elemental Abundances ◽  
Type Ia ◽  
Gaia Dr2 ◽  
Rule Out

ABSTRACT Observations of stellar remnants linked to Type Ia and Type Iax supernovae are necessary to fully understand their progenitors. Multiple progenitor scenarios predict a population of kicked donor remnants and partially burnt primary remnants, both moving with relatively high velocity. But only a handful of examples consistent with these two predicted populations have been observed. Here we report the likely first known example of an unbound white dwarf that is consistent with being the fully cooled primary remnant to a Type Iax supernova. The candidate, LP 93-21, is travelling with a galactocentric velocity of $v_{\textrm {gal}} \simeq 605\, {\rm km}\, {\rm s}^{-1}$, and is gravitationally unbound to the Milky Way. We rule out an extragalactic origin. The Type Iax supernova ejection scenario is consistent with its peculiar unbound trajectory, given anomalous elemental abundances are detected in its photosphere via spectroscopic follow-up. This discovery reflects recent models that suggest stellar ejections likely occur often. Unfortunately the intrinsic faintness of white dwarfs, and the uncertainty associated with their direct progenitor systems, makes it difficult to detect and confirm such donors.

scholarly journals Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES

2019 ◽  
Vol 621 ◽  
pp. A49 ◽  
Author(s):  
R. Cloutier ◽  
N. Astudillo-Defru ◽  
R. Doyon ◽  
X. Bonfils ◽  
J.-M. Almenara ◽  
...  
Keyword(s):  
Time Series ◽  
Radial Velocity ◽  
Model Comparison ◽  
Planetary System ◽  
Radial Velocities ◽  
Time Sampling ◽  
Stellar Activity ◽  
Detailed Model ◽  
Self Consistent

In an earlier campaign to characterize the mass of the transiting temperate super-Earth K2-18b with HARPS, a second, non-transiting planet was posited to exist in the system at ~9 days. Further radial velocity follow-up with the CARMENES spectrograph visible channel revealed a much weaker signal at 9 days, which also appeared to vary chromatically and temporally, leading to the conclusion that the origin of the 9-day signal was more likely related to stellar activity than to a planetary presence. Here we conduct a detailed reanalysis of all available RV time-series – including a set of 31 previously unpublished HARPS measurements – to investigate the effects of time-sampling and of simultaneous modelling of planetary plus activity signals on the existence and origin of the curious 9-day signal. We conclude that the 9-day signal is real and was initially seen to be suppressed in the CARMENES data due to a small number of anomalous measurements, although the exact cause of these anomalies remains unknown. Investigation of the signal’s evolution in time with wavelength and detailed model comparison reveals that the 9-day signal is most likely planetary in nature. Using this analysis, we reconcile the conflicting HARPS and CARMENES results and measure precise and self-consistent planet masses of mp,b = 8.63 ± 1.35 and mp,c sinic = 5.62 ± 0.84 Earth masses. This work, along with the previously published RV papers on the K2-18 planetary system, highlights the importance of understanding the time-sampling and of modelling the simultaneous planet plus stochastic activity, particularly when searching for sub-Neptune-sized planets with radial velocities.

scholarly journals Gaia-DR2 extended kinematical maps

2020 ◽  
Vol 642 ◽  
pp. A95 ◽  
Author(s):  
Ž. Chrobáková ◽  
M. López-Corredoira ◽  
F. Sylos Labini ◽  
H.-F. Wang ◽  
R. Nagy
Keyword(s):  
Dark Matter ◽  
Radial Velocity ◽  
Rotation Curve ◽  
Milky Way ◽  
Galactic Plane ◽  
Dark Matter Halo ◽  
Disk Galaxies ◽  
Modified Newtonian Dynamics ◽  
Outer Disk ◽  
Gaia Dr2

Context. Recent statistical deconvolution methods have produced extended kinematical maps in a range of heliocentric distances that are a factor of two to three larger than those analysed in Gaia Collaboration (2018, A&A, 616, A11) based on the same data. Aims. In this paper, we use such maps to derive the rotation curve both in the Galactic plane and in off-plane regions and to analyse the density distribution. Methods. By assuming stationary equilibrium and axisymmetry, we used the Jeans equation to derive the rotation curve. Then we fit it with density models that include both dark matter and predictions of the MOND (Modified Newtonian dynamics) theory. Since the Milky Way exhibits deviations from axisymmetry and equilibrium, we also considered corrections to the Jeans equation. To compute such corrections, we ran N-body experiments of mock disk galaxies where the departure from equilibrium becomes larger as a function of the distance from the centre. Results. The rotation curve in the outer disk of the Milky Way that is constructed with the Jeans equation exhibits very low dependence on R and z and it is well-fitted both by dark matter halo and MOND models. The application of the Jeans equation for deriving the rotation curve, in the case of the systems that deviate from equilibrium and axisymmetry, introduces systematic errors that grow as a function of the amplitude of the average radial velocity. In the case of the Milky Way, we can observe that the amplitude of the radial velocity reaches ∼10% that of the azimuthal one at R ≈ 20 kpc. Based on this condition, using the rotation curve obtained from the Jeans equation to calculate the mass may overestimate its measurement.

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