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.

The galactic habitable zone in elliptical galaxies

2012 ◽  
Vol 11 (3) ◽  
pp. 157-161 ◽  
Author(s):  
Falguni Suthar ◽  
Christopher P. McKay
Keyword(s):  
Milky Way ◽  
Planet Formation ◽  
Elliptical Galaxies ◽  
Extrasolar Planet ◽  
Habitable Zone ◽  
Milky Way Galaxy ◽  
Habitable Zones ◽  
Nearby Stars ◽  
Host Stars ◽  
Metallicity Distribution

AbstractThe concept of a Galactic Habitable Zone (GHZ) was introduced for the Milky Way galaxy a decade ago as an extension of the earlier concept of the Circumstellar Habitable Zone. In this work, we consider the extension of the concept of a GHZ to other types of galaxies by considering two elliptical galaxies as examples, M87 and M32. We argue that the defining feature of the GHZ is the probability of planet formation which has been assumed to depend on the metallicity. We have compared the metallicity distribution of nearby stars with the metallicity of stars with planets to document the correlation between metallicity and planet formation and to provide a comparison to other galaxies. Metallicity distribution, based on the [Fe/H] ratio to solar, of nearby stars peaks at [Fe/H]≈−0.2 dex, whereas the metallicity distribution of extrasolar planet host stars peaks at [Fe/H]≈+0.4 dex. We compare the metallicity distribution of extrasolar planet host stars with the metallicity distribution of the outer star clusters of M87 and M32. The metallicity distribution of stars in the outer regions of M87 peaks at [Fe/H]≈−0.2 dex and extends to [Fe/H]≈+0.4 dex, which seems favourable for planet formation. The metallicity distribution of stars in the outer regions of M32 peaks at [Fe/H]≈−0.2 dex and extends to a much lower [Fe/H]. Both elliptical galaxies met the criteria of a GHZ. In general, many galaxies should support habitable zones.

scholarly journals Gaia DR2 in 6D: searching for the fastest stars in the Galaxy

2018 ◽  
Vol 490 (1) ◽  
pp. 157-171 ◽  
Author(s):  
T Marchetti ◽  
E M Rossi ◽  
A G A Brown
Keyword(s):  
Milky Way ◽  
Small Sample Size ◽  
European Space Agency ◽  
Small Sample ◽  
Radial Velocities ◽  
Orbital Parameter ◽  
Galactic Centre ◽  
Space Agency ◽  
The Galaxy ◽  
Orbit Integration

ABSTRACT We search for the fastest stars in the subset of stars with radial velocity measurements of the second data release (DR2) of the European Space Agency mission Gaia. Starting from the observed positions, parallaxes, proper motions, and radial velocities, we construct the distance and total velocity distribution of more than 7 million stars in our Milky Way, deriving the full 6D phase space information in Galactocentric coordinates. These information are shared in a catalogue, publicly available at http://home.strw.leidenuniv.nl/~marchetti/research.html. To search for unbound stars, we then focus on stars with a probability greater than $50 $ per cent of being unbound from the Milky Way. This cut results in a clean sample of 125 sources with reliable astrometric parameters and radial velocities. Of these, 20 stars have probabilities greater than 80 per cent of being unbound from the Galaxy. On this latter subsample, we perform orbit integration to characterize the stars’ orbital parameter distributions. As expected given the relatively small sample size of bright stars, we find no hypervelocity star candidates, stars that are moving on orbits consistent with coming from the Galactic Centre. Instead, we find seven hyperrunaway star candidates, coming from the Galactic disc. Surprisingly, the remaining 13 unbound stars cannot be traced back to the Galaxy, including two of the fastest stars (around 700 km s−1). If conformed, these may constitute the tip of the iceberg of a large extragalactic population or the extreme velocity tail of stellar streams.

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 Present state and promises to unravel the structure and kinematics of the Milky Way with the RAVE survey

2008 ◽  
Vol 4 (S254) ◽  
pp. 453-460 ◽  
Author(s):  
M. Steinmetz ◽  
A. Siebert ◽  
T. Zwitter ◽  
Keyword(s):  
Milky Way ◽  
Large Fraction ◽  
Radial Velocities ◽  
Schmidt Telescope ◽  
Milky Way Galaxy ◽  
Giant Stars ◽  
The Galaxy ◽  
Second Year ◽  
Scientific Results ◽  
First Time

AbstractThe RAdial Velocity Experiment (RAVE) is an ambitious survey to measure the radial velocities, temperatures, surface gravities, metallicities and abundance ratios for up to a million stars using the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO), over the period 2003–2011. The survey represents a big advance in our understanding of our own Milky Way galaxy. The main data product will be a southern hemisphere survey of about a million stars. Their selection is based exclusively on their I–band colour, so avoiding any colour-induced bias. RAVE is expected to be the largest spectroscopic survey of the Solar neighbourhood in the coming decade, but with a significant fraction of giant stars reaching out to 10 kpc from the Sun. RAVE offers the first truly representative inventory of stellar radial velocities for all major components of the Galaxy. Here we present the first scientific results of this survey as well as its second data release which doubles the number of previously released radial velocities. For the first time, the release also provides atmospheric parameters for a large fraction of the second year data, making it an unprecedented tool to study the formation of the Milky Way. Plans for further data releases are outlined.

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 Spectroscopy of Red Giants of the Sagittarius Dwarf Galaxy

1999 ◽  
Vol 192 ◽  
pp. 129-135
Author(s):  
G. Marconi ◽  
P. Bonifacio ◽  
L. Pasquini ◽  
P. Molaro
Keyword(s):  
Star Formation ◽  
Radial Velocity ◽  
Dwarf Galaxy ◽  
Spectral Synthesis ◽  
Radial Velocities ◽  
Red Giants ◽  
Photometric Study ◽  
Ccd Photometry

The photometric study of the Sagittarius dwarf galaxy by Marconi et al. (1998) has suggested the presence of a spread in metallicity (-0.7 ≤ [Fe/H] ≤ −1.6), which may result from different bursts of star formation. We present the results from a Multi Object Slit spectroscopy program carried out at the NTT with the aim to determine spectroscopic abundances of Sagittarius giants selected from the CCD photometry. From our intermediate resolution (R~1500) spectra, radial velocities are determined to confirm the membership and metallicities are derived by using spectral synthesis codes for stars down to V ~ 18, i.e. below the RGB clump. Out of 57 observed stars, 23 have a radial velocity consistent with Sagittarius membership; here we present results for 8 of these. No star with [Fe/H]< −1.0 is found, three stars are found to be metal-rich.

scholarly journals Hot Horizontal-Branch Stars in the Galactic Bulge

1999 ◽  
Vol 192 ◽  
pp. 395-401
Author(s):  
D. M. Terndrup ◽  
R. C. Peterson ◽  
E. M. Sadler ◽  
A. R. Walker
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Radial Velocities ◽  
Ultraviolet Excess ◽  
Horizontal Branch ◽  
Galactic Bulge ◽  
Horizontal Branch Stars ◽  
Star Studies

We report the discovery of hot horizontal branch stars in the nuclear bulge of the Milky Way. Spectra from the 2dF instrument of the Anglo-Australian Telescope allow us to confirm their membership in the bulge through radial velocities. We also review the current observational information on hot horizontal branch stars in Milky Way clusters and the Local Group, and discuss the relevance of star-by-star studies in the bulge for the ultraviolet-excess phenomenon seen in large ellipticals.

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 M Giant Kinematics in Off-Axis Fields Between 150 and 300 PC from the Galactic Center

1996 ◽  
Vol 169 ◽  
pp. 111-117
Author(s):  
R. D. Blum ◽  
J. S. Carr ◽  
K. Sellgren ◽  
D. M. Terndrup
Keyword(s):  
Radial Velocity ◽  
Velocity Dispersion ◽  
Galactic Center ◽  
Radial Velocities ◽  
Galactic Bulge ◽  
Mass Model ◽  
The Mean

We present radial velocities for approximately 40 stars in each of four optically obscured, off-axis fields toward the Galactic bulge. The mean heliocentric radial velocity and velocity dispersion are −75 ± 24 km s–1 and 127 ± 16 km s–1 2 ± 23 km s–1 and 127 ± 14 km s–1, −14 ± 22 km s–1 and 126 ± 14 km s–1, and −31 ± 28 km s–1 and 153 ± 17 km s–1 for fields located at 299, 288, 171, and 160 pc projected radius, respectively. The dispersions generally match Kent's (1992) axisymmetric mass model but may be higher than the model's predictions at small projected radius.

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