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 The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way

2018 ◽  
Vol 616 ◽  
pp. L9 ◽  
Author(s):  
G. Monari ◽  
B. Famaey ◽  
I. Carrillo ◽  
T. Piffl ◽  
M. Steinmetz ◽  
...  
Keyword(s):  
Mass Concentration ◽  
Milky Way ◽  
Galactic Centre ◽  
High Concentration ◽  
Circular Velocity ◽  
Halo Stars ◽  
Dark Matter Mass ◽  
The Galaxy ◽  
Escape Speed ◽  
Gaia Dr2

We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of ~2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactocentric radii ranging from ~5 kpc to ~10.5 kpc. The local Galactic escape at the Sun’s position is estimated to be ve(r⊙) = 580 ± 63 km s−1, and it rises towards the Galactic centre. Defined as the minimum speed required to reach three virial radii, our estimate of the escape speed as a function of radius implies for a Navarro–Frenk–White profile and local circular velocity of 240 km s−1 a dark matter mass M200 = 1.28−0.50+0.68 × 1012 M⊙ and a high concentration c200 = 11.09−1.79+2.94. Assuming the mass-concentration relation of ΛCDM, we obtain M200 = 1.55−0.51+0.64 × 1012 M⊙ and c200 = 7.93−0.27+0.33 for a local circular velocity of 228 km s−1.

Connectionist Systems and Signal Processing Techniques Applied to the Parameterization of Stellar Spectra

2010 ◽  
pp. 187-203
Author(s):  
Diego Ordóñez ◽  
Carlos Dafonte ◽  
Bernardino Arcay ◽  
Minia Manteiga
Keyword(s):  
Effective Temperature ◽  
Wavelet Transforms ◽  
European Space Agency ◽  
Wavelength Region ◽  
Atmospheric Parameter ◽  
Automated Classification ◽  
Stellar Spectra ◽  
Additional Information ◽  
Space Agency ◽  
The Galaxy

A stellar spectrum is the finger-print identification of a particular star, the result of the radiation transport through its atmosphere. The physical conditions in the stellar atmosphere, its effective temperature, surface gravity, and the presence and abundance of chemical elements explain the observed features in the stellar spectra, such as the shape of the overall continuum and the presence and strength of particular lines and bands. The derivation of the atmospheric stellar parameters from a representative sample of stellar spectra collected by ground-based and spatial telescopes is essential when a realistic view of the Galaxy and its components is to be obtained. In the last decade, extensive astronomical surveys recording information of large portions of the sky have become a reality since the development of robotic or semi-automated telescopes. The Gaia satellite is one of the key missions of the European Space Agency (ESA) and its launch is planned for 2011. Gaia will carry out the so-called Galaxy Census by extracting precise information on the nature of its main constituents, including the spectra of objects (Wilkinson, 2005). Traditional methods for the extraction of the fundamental atmospheric stellar parameters (effective temperature (Teff), gravity (log G), metallicity ([Fe/H]), and abundance of alpha elements [a/Fe], elements integer multiples of the mass of the helium nucleus) are time-consuming and unapproachable for a massive survey involving 1 billion objects (about 1% of the Galaxy constituents) such as Gaia. This work presents the results of the authors’ study and shows the feasibility of an automated extraction of the previously mentioned stellar atmospheric parameters from near infrared spectra in the wavelength region of the Gaia Radial Velocity Spectrograph (RVS). The authors’ approach is based on a technique that has already been applied to problems of the non-linear parameterization of signals: artificial neural networks. It breaks ground in the consideration of transformed domains (Fourier and Wavelet Transforms) during the preprocessing stage of the spectral signals in order to select the frequency resolution that is best suited for each atmospheric parameter. The authors have also progressed in estimating the noise (SNR) that blurs the signal on the basis of its power spectrum and the application of noise-dependant algorithms of parameterization. This study has provided additional information that allows them to progress in the development of hybrid systems devoted to the automated classification of stellar spectra.

scholarly journals Mass of the Milky Way

2004 ◽  
Vol 220 ◽  
pp. 213-214
Author(s):  
O. I. Wong ◽  
M. J. Drinkwater ◽  
J. B. Jones ◽  
M. D. Gregg ◽  
K. C. Freeman
Keyword(s):  
Milky Way ◽  
Galactic Centre ◽  
Escape Velocity ◽  
The Galaxy

We present a new estimate of the mass of the Milky Way based on the escape velocity of a sample of distant stars, about 12 kpc from the Galactic centre and about 5 kpc from the plane of the Galaxy. Our sample is very different from previous escape-velocity studies, being compiled from an all-object spectroscopic survey of a region of sky. the derived mass within 12 kpc of the Galactic centre is (1.3 ±0.3) × 1011M⊙.

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 Around Gaia Alerts in 20 questions

2011 ◽  
Vol 7 (S285) ◽  
pp. 425-428 ◽  
Author(s):  
Łukasz Wyrzykowski ◽  
Simon Hodgkin
Keyword(s):  
Data Stream ◽  
European Space Agency ◽  
Space Mission ◽  
Proper Motions ◽  
Space Agency ◽  
Large Numbers ◽  
Formation History ◽  
The Galaxy ◽  
Optical Wavelengths ◽  
Astrometric Data

AbstractGaia is a European Space Agency (ESA) astrometry space mission, and a successor to the ESA Hipparcos mission. Gaia's main goal is to collect high-precision astrometric data (positions, parallaxes, and proper motions) for the 1 billion brightest objects in the sky. Those data, complemented with multi-band, multi-epoch photometric and spectroscopic data observed from the same observing platform, will allow astronomers to reconstruct the formation history, structure, and evolution of the Galaxy.Gaia will observe the whole sky for 5 years, providing a unique opportunity for the discovery of large numbers of transient and anomalous events such as supernovæ, novæ and microlensing events, GRB afterglows, fallback supernovæ, and other theoretical or unexpected phenomena. The Photometric Science Alerts team has been tasked with the early detection, classification and prompt release of anomalous sources in the Gaia data stream. In this paper we discuss the challenges we face in preparing to use Gaia to search for transient pheonomena at optical wavelengths.

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 The science of EChO

2010 ◽  
Vol 6 (S276) ◽  
pp. 359-370 ◽  
Author(s):  
Giovanna Tinetti ◽  
James Y-K. Cho ◽  
Caitlin A. Griffith ◽  
Olivier Grasset ◽  
Lee Grenfell ◽  
...  
Keyword(s):  
Solar System ◽  
Emission Spectroscopy ◽  
European Space Agency ◽  
Habitable Zone ◽  
The Past ◽  
Space Agency ◽  
Kepler Mission ◽  
The Galaxy ◽  
Earth Like Planets ◽  
Exoplanetary Atmospheres

AbstractThe science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.

scholarly journals The RAVE harvest: from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra

2013 ◽  
Vol 9 (S298) ◽  
pp. 292-297
Author(s):  
Corrado Boeche ◽  
Keyword(s):  
Milky Way ◽  
Radial Velocities ◽  
Proper Motions ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Chemical Gradients ◽  
Single Process ◽  
The Galaxy ◽  
Nearby Stars ◽  
Kinematic Information

AbstractRAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk using RAVE data and compare our results with the Besançon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

scholarly journals 3D N-Body Simulations of the Milky Way

1996 ◽  
Vol 169 ◽  
pp. 125-131 ◽  
Author(s):  
R. Fux ◽  
L. Martinet ◽  
D. Pfenniger
Keyword(s):  
Milky Way ◽  
Position Angle ◽  
Angular Speed ◽  
Galactic Centre ◽  
Mass Model ◽  
Axis Ratio ◽  
Ongoing Work ◽  
The Galaxy ◽  
Kinematical Data ◽  
Extension Axis

While the existence of a central bar in our Galaxy now seems to be well established, its parameters (such as position angle, extension, axis ratio, angular speed etc…) still remain controversial. The large amount of photometrical and stellar kinematical data becoming now available within ∼ 30° of the Galactic Centre should provide potentially new constraints on these parameters. Unfortunately, a detailed barred model of the Milky Way, which would offer a powerful work frame to interpret such observations, does not exist yet. We therefore report here on a first attempt at constructing a 3D dynamically self-consistent barred model of the Galaxy. The idea is to follow the time evolution of a set of 400,000 particles initially distributed according to a plausible axisymmetric mass model of the Milky Way and in virial equilibrium, hoping that a bar will form spontaneously. Gas is not included so far, but will be introduced as a next step in this ongoing work. Some results presented at this meeting will be only quickly summarised here and explained in some more details elsewhere (Fux et al. 1995 and A&A paper in preparation).

Radial Velocity Measurements with Objective Prisms for the Hipparcos Program

1984 ◽  
Vol 88 ◽  
pp. 196-198
Author(s):  
Ch. Fehrenbach
Keyword(s):  
Radial Velocity ◽  
European Space Agency ◽  
Stellar Dynamics ◽  
High Accuracy ◽  
Radial Velocities ◽  
High Dispersion ◽  
Proper Motions ◽  
Space Agency ◽  
Nearby Stars ◽  
Absolute Magnitudes

In 1986, the European Space Agency (ESA) will launch an astrometrie satellite, Hipparcos (see ESA SP-177) with the objective of measuring positions for 200,000 stars. Proper motions will be determined with an accuracy of 0.002 "/yr. It is also very important to have radial velocities for the program stars.We will show here that an accuracy of 4 to 5 km/s for the radial velocity is good enough for a number of studies. For stellar studies, we need highly accurate radial velocities, and correlation methods (Griffin, Mayor et al.) allow that but are restricted to cool stars. Radial velocities are also needed for studies of stellar dynamics. In the case of star clusters (open and globular) we need a high accuracy, however the study of motions of stars in our galaxy do not require such a high accuracy. Only by increasing the sample can we improve our knowledge. In Table I we give data for the velocity ellipsoid. Kinematical data are from Allen and we have added absolute magnitudes and distances for stars having mv = 7.5. From an examination of this table we see that an accuracy of 4-5 km/s is good enough to study B star motions. The last column gives the dispersion in proper motion, and some of the values are astonishing, but it is well known that the proper motions for the nearby stars show a very high dispersion.

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