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J/MNRAS/397/1748    Spectroscopic study of Segue 2           (Belokurov+, 2009)

The discovery of Segue 2: a prototype of the population of satellites of satellites. Belokurov V., Walker M.G., Evans N.W., Gilmore G., Irwin M.J., Mateo M., Mayer L., Olszewski E., Bechtold J., Pickering T. <Mon. Not. R. Astron. Soc., 397, 1748-1755 (2009)> =2009MNRAS.397.1748B
ADC_Keywords: Galaxies, nearby ; Photometry, SDSS ; Radial velocities Keywords: galaxies: dwarf - galaxies: individual: Segue 2 - Local Group Abstract: We announce the discovery of a new Milky Way satellite Segue 2 found in the data of the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We followed this up with deeper imaging and spectroscopy on the Multiple Mirror Telescope (MMT). From this, we derive a luminosity of Mv=-2.5, a half-light radius of 34pc and a systemic velocity of ~-40km/s. Our data also provide evidence for a stream around Segue 2 at a similar heliocentric velocity, and the SEGUE data show that it is also present in neighbouring fields. We resolve the velocity dispersion of Segue 2 as 3.4km/s and the possible stream as ∼7km/s. This object shows points of comparison with other recent discoveries, Segue 1, Boo II and Coma. We speculate that all four objects may be representatives of a population of satellites of satellites - survivors of accretion events that destroyed their larger but less dense parents. They are likely to have formed at redshifts z>10 and are good candidates for fossils of the reionization epoch. Description: Follow-up imaging of Segue 2 was carried out on 2007 October 7 using the Megacam imager on the Multiple Mirror Telescope (MMT). On 2008 October 22-23 and 26, we obtained high-resolution spectra of 352 targets around Segue 2 using three independent fibre configurations with the Hectochelle spectrograph at the MMT. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 73 422 Hectochelle spectroscopy of Segue 2
See also: J/ApJ/694/L144 : Spectroscopic study of Leo V (Walker+, 2009) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 5 A5 --- --- [Seg2-] 6- 8 I03 --- Seq Number in galaxy 10- 11 I2 h RAh Rihgt ascension (J2000) 13- 14 I2 min RAm Rihgt ascension (J2000) 16- 20 F5.2 s RAs Rihgt ascension (J2000) 22 A1 --- DE- Declination sign (J2000) 23- 24 I2 deg DEd Declination (J2000) 26- 27 I2 arcmin DEm Declination (J2000) 29- 32 F4.1 arcsec DEs Declination (J2000) 34- 37 F4.1 arcmin R Angular radius from Segue 2 center 39- 43 F5.2 mag gmag g magnitude 45- 49 F5.2 mag imag i magnitude 51- 56 F6.1 km/s HV Heliocentric velocity 58- 60 F3.1 km/s e_HV rms uncertainty on HV 62- 66 F5.2 0.1nm sigMg ? Composite magnesium index (1) 68- 71 F4.2 0.1nm e_sigMg ? rms uncertainty on sigMg 73 A1 --- Mm [BSY?N] Membership status (2)
Note (1): Weighted sum of pseudo-equivalent widths for each individual line of the Mg-I/Mg-b triplet (see Walker et al., 2007ApJS..171..389W). Note (2): Membership flag as follows: Y = member, on the bright part of the RGB (5 stars) N = no association with Segue 2 ? = possible member from the fainter region of the RGB (3 stars) B = blue horizontal branch (BHB) member (3 stars) S = stream candidate (15 stars)
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Nov-2009
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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