Sonia Duffau

Publications (3)6.02 Total impact

• Source

  Available from: Zeljko Ivezic

  Article: Halo Velocity Groups in the Pisces Overdensity

  Branimir Sesar, A. Katherina Vivas, Sonia Duffau, Zeljko Ivezic
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  ABSTRACT: We report spectroscopic observations with the Gemini South Telescope of 5 faint V~20 RR Lyrae stars associated with the Pisces overdensity. At a heliocentric and galactocentric distance of ~80 kpc, this is the most distant substructure in the Galactic halo known to date. We combined our observations with literature data and confirmed that the substructure is composed of two different kinematic groups. The main group contains 8 stars and has <V_{gsr}> = 50 km/s, while the second group contains four stars at a velocity of <V_{gsr}> = -52 km/s, where V_{gsr} is the radial velocity in the galactocentric standard of rest. The metallicity distribution of RR Lyrae stars in the Pisces overdensity is centered on [Fe/H]=-1.5 dex and has a width of 0.3 dex. The new data allowed us to establish that both groups are spatially extended making it very unlikely that they are bound systems, and are more likely to be debris of a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still unclear whether these groups have the same or different progenitors. Comment: 21 pages, 5 figures, 3 tables, accepted to Astrophysical Journal
  05/2010;
• Source

  Available from: cida.gob.ve

  Article: Spectroscopy of QUEST RR Lyrae Variables: The New Virgo Stellar Stream

  Sonia Duffau, Robert Zinn, A. Katherina Vivas, Giovanni Carraro, René A. Méndez, Rebeccah Winnick, and Carme Gallart
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  ABSTRACT: Eighteen RR Lyrae variables (RRLs) that lie in the "124 clump" identified by the Quasar Equatorial Survey Team (QUEST) have been observed spectroscopically to measure their radial velocities and metal abundances. Ten blue horizontal branch (BHB) stars identified by the Sloan Digital Sky Survey (SDSS) were added to this sample. Six of the nine stars in the densest region of the clump have a mean radial velocity in the Galactic rest frame (Vgsr) of 99.8 and σ = 17.3 km s-1, which is slightly smaller than the average error of the measurements. The whole sample contains eight RRLs and five BHB stars that have values of Vgsr suggesting membership in this stream. For seven of these RRLs, the measurements of [Fe/H], which have an internal precision of 0.08 dex, yield [Fe/H] = -1.86 and σ = 0.40. These values suggest that the stream is a tidally disrupted dwarf spheroidal galaxy of low luminosity. Photometry from the database of the SDSS indicates that this stream covers at least 106 deg2 of the sky in the constellation Virgo. The name Virgo stellar stream is suggested.
  The Astrophysical Journal 12/2008; 636(2):L97. · 6.02 Impact Factor
• Source

  Available from: ArXiv

  Article: Spectroscopy of bright quest RR Lyrae stars: Velocity substructures toward Virgo

  A. Katherina Vivas, Yara L. Jaff´, Robert Zinn, Rebeccah Winnick, Sonia Duffau, Cecilia Mateu
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  ABSTRACT: Using a sample of 43 bright (V < 16.1, distance < 13 kpc) RR Lyrae stars (RRLS) from the QUEST survey with spectroscopic radial velocities and metallicities, we find that several separate halo substructures contribute to the Virgo overdensity (VOD). While there is little evidence for halo substructure in the spatial distribution of these stars, their distribution in radial velocity reveals two moving groups. These results are reinforced when the sample is combined with a sample of blue horizontal branch stars that were identified in the SDSS, and the combined sample provides evidence for one additional moving group. These groups correspond to peaks in the radial velocity distribution of a sample of F type main-sequence stars that was recently observed in the same directon by SEGUE, although in one case the RRLS and F star groups may not lie at the same distance. One of the new substructures has a very narrow range in metallicity, which is more consistent with it being the debris from a destroyed globular cluster than from a dwarf galaxy. A small concentration of stars have radial velocities that are similar to the Virgo Stellar Stream (VSS) that was identified previously in a fainter sample of RRLS. Our results suggest that this feature extends to distances as short as ∼ 12 kpc from its previous detection at ∼ 19 kpc. None of the new groups and only one star in the sample have velocities that are consistent with membership in the leading tidal stream from the Sagittarius Dwarf Spheroidal Galaxy, which some authors have suggested is the origin of the VOD. This research was supported by the National Science Foundation under grants AST 00-98428 and AST 05-07364.