J/ApJ/784/19 Orphan stream high-resolution spectroscopic study (Casey+, 2014)
Hunting the parent of the Orphan stream.
II. The first high-resolution spectroscopic study.
Casey A.R., Keller S.C., Da Costa G., Frebel A., Maunder E.
<Astrophys. J., 784, 19 (2014)>
=2014ApJ...784...19C 2014ApJ...784...19C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, halo ; Equivalent widths ; Abundances
Keywords: Galaxy: halo - Galaxy: structure - stars: abundances -
stars: late-type - stars: Population II
Abstract:
We present the first high-resolution spectroscopic study on the Orphan
stream for five stream candidates, observed with the Magellan Inamori
Kyocera Echelle spectrograph on the Magellan Clay telescope. The
targets were selected from the low-resolution catalog of Casey et al.
(2013ApJ...764...39C 2013ApJ...764...39C): three high-probability members, one medium, and
one low-probability stream candidate were observed. Our analysis
indicates that the low- and medium-probability targets are metal-rich
field stars. The remaining three high-probability targets range over
∼1 dex in metallicity, and are chemically distinct compared to the
other two targets and all standard stars: low [α/Fe] abundance
ratios are observed, and lower limits are ascertained for [Ba/Y],
which sit well above the Milky Way trend. These chemical signatures
demonstrate that the undiscovered parent system is unequivocally a
dwarf spheroidal galaxy, consistent with dynamical constraints
inferred from the stream width and arc. As such, we firmly exclude the
proposed association between NGC 2419 and the Orphan stream. A wide
range in metallicities adds to the similarities between the Orphan
stream and Segue 1, although the low [α/Fe] abundance ratios in
the Orphan stream are in tension with the high [α/Fe] values
observed in Segue 1. Open questions remain before Segue 1 could
possibly be claimed as the "parent" of the Orphan stream. The parent
system could well remain undiscovered in the southern sky.
Description:
High-resolution spectra for five Orphan stream candidates and seven
well-studied standard stars have been obtained with the Magellan
Inamori Kyocera Echelle spectrograph (Bernstein et al.
2003SPIE.4841.1694B 2003SPIE.4841.1694B) on the Magellan Clay telescope. These objects
were observed in 2011 March using a 1" wide slit in mean seeing of
0.9". This slit configuration provides continuous spectral coverage
from 333 nm to 915 nm, with a spectral resolution of R=25000 in the blue
arm and R=28000 in the red arm. A minimum of 10 exposures of each
calibration type (biases, flat fields, and diffuse flats) were
observed in the afternoon of each day, with additional flat-field and
Th-Ar arc lamp exposures performed throughout the night to ensure an
accurate wavelength calibration.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 12 Observations
table2.dat 103 499 Equivalent Widths for Standard and Program Stars
table6.dat 48 280 Abundance Uncertainties Due to Stellar
Parameters
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See also:
J/AJ/120/1841 : Abundances and Kinematics of Halo and Disk Stars
(Fulbright 2000)
J/ApJ/698/865 : Halo streams in the SDSS-DR7 (Klement+, 2009)
J/ApJ/711/573 : Detailed abundances in a halo stellar stream (Roederer+, 2010)
J/ApJ/776/26 : RRab stars in the Orphan stream distances (Sesar+, 2013)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star identifier (HD NNNNNN, OSS-NN)
10 A1 --- n_Name [LMH] Note on Name (1)
12- 13 I2 h RAh Hour of Right Ascension (J2000)
15- 16 I2 min RAm Minute of Right Ascension (J2000)
18- 21 F4.1 s RAs Second of Right Ascension (J2000)
23 A1 --- DE- Sign of the Declination (J2000)
24- 25 I2 deg DEd Degree of Declination (J2000)
27- 28 I2 arcmin DEm Arcminute of Declination (J2000)
30- 33 F4.1 arcsec DEs Arcsecond of Declination (J2000)
35- 39 F5.2 mag Vmag [5.86/17.82] V-band magnitude (2)
41- 50 A10 "date" Date UT Date of observation
52- 59 A8 "h:m:s" Time UT Time of observation
61- 64 F4.2 --- Airmass [1.01/2.0] Airmass
66- 72 A7 s Exp Exposure time
74- 76 I3 --- S/N [31/335] Signal-to-noise ratio (3)
79- 83 F5.1 km/s HV [-38.2/297.8] Heliocentric velocity
85- 87 F3.1 km/s e_HV [0.9/1.3] Heliocentric velocity error
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Note (1): Probability of membership (low, medium, high) listed for the Orphan
stream candidates as defined by Casey et al. (2013ApJ...764...39C 2013ApJ...764...39C).
Note (2): V-band magnitudes for the Orphan stream targets are estimated to be
equivalent to g-band magnitudes.
Note (3): S/N measured per pixel (∼0.09 Å/pixel) at 600 nm for each target.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 nm Wave Wavelength
10- 13 F4.1 --- Species [8.0/63.1] Species identifier
15- 18 F4.2 eV chi Excitation potential
20- 26 F7.3 [-] log(gf) Log of the oscillator strength
28- 33 F6.2 10-13m HD41667 ? HD 41667 equivalent width (1)
35- 40 F6.2 10-13m HD44007 ? HD 44007 equivalent width (1)
42- 47 F6.2 10-13m HD76932 ? HD 76932 equivalent width (1)
49- 54 F6.2 10-13m HD136316 ? HD 136316 equivalent width (1)
56- 61 F6.2 10-13m HD141531 ? HD 141531 equivalent width (1)
63- 68 F6.2 10-13m HD142948 ? HD 142948 equivalent width (1)
70- 75 F6.2 10-13m OSS-3 ? OSS 3 equivalent width (1)
77- 82 F6.2 10-13m OSS-6 ? OSS 6 equivalent width (1)
84- 89 F6.2 10-13m OSS-8 ? OSS 8 equivalent width (1)
91- 96 F6.2 10-13m OSS-14 ? OSS 14 equivalent width (1)
98-103 F6.2 10-13m OSS-18 ? OSS 18 equivalent width (1)
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Note (1): In units of milli-Angstroms.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star identifier (HD NNNNNN, OSS-NN)
11- 15 A5 --- Species Species identifier
17- 21 F5.2 [-] DATeff Abundance uncertainty from Teff
23- 27 F5.2 [-] DAlogg Abundance uncertainty from log(g)
29- 33 F5.2 [-] DAvt Abundance uncertainty from microturbulence
35- 38 F4.2 [-] SEDrand Abundance random standard error about the mean
40- 43 F4.2 [-] e_[X/H] Total [X/H] abundance uncertainty
45- 48 F4.2 [-] e_[X/Fe] ? Total [X/Fe] abundance uncertainty
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History:
From electronic version of the journal
References:
Casey et al., Paper I, 2013ApJ...764...39C 2013ApJ...764...39C
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 27-Jun-2017