J/AJ/152/58 CaII spectroscopy of SMC red giants. IV. (Parisi+, 2016)
Ca II triplet spectroscopy of Small Magellanic Cloud red giants. IV. Abundances
for a large sample of field stars and comparison with the cluster sample.
Parisi M.C., Geisler D., Carraro G., Claria J.J., Villanova S.,
Gramajo L.V., Sarajedini A., Grocholski A.J.
<Astron. J., 152, 58-58 (2016)>
=2016AJ....152...58P 2016AJ....152...58P (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Associations, stellar ; Stars, giant ;
Abundances, [Fe/H] ; Equivalent widths
Keywords: galaxies: stellar content - Magellanic Clouds - stars: abundances
Abstract:
This paper represents a major step forward in the systematic and
homogeneous study of Small Magellanic Cloud (SMC) star clusters and
field stars carried out by applying the calcium triplet technique. We
present in this work the radial velocity and metallicity of
approximately 400 red giant stars in 15 SMC fields, with typical
errors of about 7km/s and 0.16dex, respectively. We added to
this information our previously determined metallicity values for 29
clusters and approximately 350 field stars using the identical
techniques. Using this enlarged sample, we analyze the metallicity
distribution and gradient in this galaxy. We also compare the chemical
properties of the clusters and of their surrounding fields. We find a
number of surprising results. While the clusters, taken as a whole,
show no strong evidence for a metallicity gradient (MG), the field
stars exhibit a clear negative gradient in the inner region of the
SMC, consistent with the recent results of Dobbie et al. For distances
to the center of the galaxy less than 4°, field stars show a
considerably smaller metallicity dispersion than that of the clusters.
However, in the external SMC regions, clusters and field stars exhibit
similar metallicity dispersions. Moreover, in the inner region of the
SMC, clusters appear to be concentrated in two groups: one more
metal-poor and another more metal-rich than field stars. Individually
considered, neither cluster group presents an MG. Most surprisingly,
the MG for both stellar populations (clusters and field stars) appears
to reverse sign in the outer regions of the SMC. The difference
between the cluster metallicity and the mean metallicity of the
surrounding field stars turns out to be a strong function of the
cluster metallicity. These results could be indicating different
chemical evolution histories for these two SMC stellar populations.
They could also indicate variations in the chemical behavior of the
SMC in its internal and external regions.
Description:
This paper is a continuation of our previous work wherein we
determined and analyzed the metallicity of 29 Small Magellanic Cloud
(SMC) clusters (Parisi et al. 2009, Cat. J/AJ/138/517; Parisi et al.
2015, Cat. J/AJ/149/154) and that of a sample of ∼350 red giant field
stars (Parisi et al. 2010, Cat. J/AJ/139/1168) surrounding the 15 SMC
star clusters studied in Parisi et al. 2009 (Cat. J/AJ/138/517). Here
we add the ∼400 red giants in 15 fields that surround the 14 star
clusters studied in Parisi et al. 2015 (Cat. J/AJ/149/154) (in Parisi
et al. 2015, Cat. J/AJ/149/154, we discard the cluster B113, but we
can still use the surrounding field stars). We repeat here the
identical procedures followed in Parisi et al. 2010 (Cat.
J/AJ/139/1168). We refer the reader to Parisi et al. 2015 (Cat.
J/AJ/149/154) for details regarding the selection of the cluster
sample, the spectroscopic targets, and the observations. The list of
the star clusters studied in Parisi et al. 2015 (Cat. J/AJ/149/154)
can be seen in Table1 of that paper.
Each cluster was centered on the master chip, while surrounding field
stars were observed in both the master and secondary CCD. Pre-images
in the V and I bands and the spectra of selected stars were obtained
as part of programs 0.82B-0505 and 384.B-0687. The selection of
spectroscopic targets was made on the corresponding (V, V-I) CMD by
choosing stars located along the red giant branch. The spectroscopic
observations were performed in service mode with the instrument FORS2
on the Very Large Telescope (VLT) in mask exchange unit mode (MXU),
with the same instrumental setup as in Grocholski et al. 2006 (Cat.
J/AJ/132/1630) and Parisi et al. 2009 (Cat. J/AJ/138/517). A very few
stars have signal-to-noise ratio (S/N)∼15pixel-1, but the remaining
targets have S/N between ∼20 and ∼80pixel-1. Information about
exposure times, size of the slits, seeing, and characteristics of the
obtained spectra can be found in Section 3 of Parisi et al. 2015 (Cat.
J/AJ/149/154).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 46 400 Measured values for field stars
table2.dat 32 15 Small Magellanic Cloud (SMC) field results
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See also:
J/AJ/149/154 : CaII spectroscopy of SMC red giants. III. (Parisi+, 2015)
J/MNRAS/449/639 : VMC survey. XIV. SFR in SMC (Rubele+, 2015)
J/MNRAS/442/1680 : Red giants in SMC. Abundances (Dobbie+, 2014)
J/MNRAS/442/1663 : Velocities of red giants in the SMC (Dobbie+, 2014)
J/AJ/139/1168 : CaII spectroscopy of SMC fields stars (Parisi+, 2010)
J/AJ/138/517 : CaII spectroscopy of SMC red giants (Parisi+, 2009)
J/AJ/136/1039 : CaII index of SMC red giant branch stars (Carrera+, 2008)
J/MNRAS/389/678 : Extended objects in Magellanic Clouds (Bica+, 2008)
J/AJ/132/1630 : CaII spectroscopy in MC clusters (Grocholski+, 2006)
J/AJ/131/2514 : Radial velocities of red giants in the SMC (Harris+, 2006)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Field Name of the selected field in SMC (G1)
9 A1 --- Chip [MS] Chip (M=Master or S=Secondary)
11- 12 I2 --- Star [1/32] Field member identification number
14- 20 F7.3 mag V-VHB [-10.4/1.5]? Brightness difference between star
and clump
22- 27 F6.3 0.1nm WCaII [3.2/11.2]? Summed Ca II equivalent width
(ΣW); in Å (1)
29- 33 F5.3 0.1nm e_WCaII [0.04/1.83]? The 1σ error in WCaII
(σΣW); in Å
35- 40 F6.3 --- [Fe/H] [-3.9/1.1]? Metallicity
42- 46 F5.3 --- e_[Fe/H] [0.07/0.68]? The error in [Fe/H]
--------------------------------------------------------------------------------
Note (1): Where WCaII=EW(8498Å)+EW(8542Å)+EW(8662Å).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Field Name of the selected field in SMC (G1)
9- 10 I2 --- Ns [9/40] Number of stars belonging to the
corresponding field
12- 16 F5.2 [Sun] [Fe/H]G [-1.3/-0.7] Peak of the fitted Gaussian function
([Fe/HG)
18- 21 F4.2 [Sun] e_[Fe/H]G [0.03/0.08] Standard error in [Fe/H]G
23- 27 F5.2 [Sun] [Fe/H]M [-1.2/-0.7] Median metallicity value ([Fe/H]M)
29- 32 F4.2 [Sun] e_[Fe/H]M [0.04/0.1] Standard error in [Fe/H]M
--------------------------------------------------------------------------------
Global Notes:
Note (G1): We add the ∼400 red giants (table1) in 15 fields that surround the
14 star clusters studied in Paper III (Parisi et al. 2015,
Cat. J/AJ/149/154) (in Paper III we discard the cluster B113, but we
can still use the surrounding field stars).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Parisi et al., Paper I 2009AJ....138..517P 2009AJ....138..517P, Cat. J/AJ/138/517
Parisi et al., Paper II 2010AJ....139.1168P 2010AJ....139.1168P, Cat. J/AJ/139/1168
Parisi et al., Paper III 2015AJ....149..154P 2015AJ....149..154P, Cat. J/AJ/149/154
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 23-Sep-2016