2006ApJ...637..269V

Query : 2006ApJ...637..269V

2006ApJ...637..269V - Astrophys. J., 637, 269-282 (2006/January-3)

Oxygen and nitrogen in Leo A and GR 8.

VAN ZEE L., SKILLMAN E.D. and HAYNES M.P.

Abstract (from CDS):

We present elemental abundances for multiple H II regions in Leo A and GR 8 obtained from long-slit optical spectroscopy of these two nearby low-luminosity dwarf irregular galaxies. As expected from their luminosities, and in agreement with previous observations, the derived oxygen abundances are extremely low in both galaxies. High signal-to-noise ratio (S/N) observations of a planetary nebula in Leo A yield 12+log(O/H)=7.30±0.05; semiempirical calculations of the oxygen abundance in four H II regions in Leo A indicate 12+log(O/H)=7.38±0.10. These results confirm that Leo A has one of the lowest ISM metal abundances of known nearby galaxies. Based on results from two H II regions with high S/N measurements of the weak [O III] λ4363 line, the mean oxygen abundance of GR 8 is 12+log(O/H)=7.65±0.06; using ``empirical'' and ``semiempirical'' methods, similar abundances are derived for six other GR 8 H II regions. Similar to previous results in other low-metallicity galaxies, the mean log(N/O)=-1.53±0.09 for Leo A and -1.51±0.07 for GR 8. There is no evidence of significant variations in either O/H or N/O in the H II regions. The metallicity-luminosity relation for nearby (D<5 Mpc) dwarf irregular galaxies with measured oxygen abundances has a mean correlation of 12+log(O/H)=5.67MB-0.151MB, with a dispersion in oxygen about the relationship of σ=0.21. These observations confirm that gas-rich, low-luminosity galaxies have extremely low elemental abundances in the ionized gas phase of their interstellar media. Although Leo A has one of the lowest metal abundances of known nearby galaxies, detection of tracers of an older stellar population (RR Lyrae variable stars, horizontal branch stars, and a well-populated red giant branch) indicate that it is not a newly formed galaxy, as has been proposed for some other similar low-metallicity star-forming galaxies.

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Journal keyword(s): Galaxies: Abundances - Galaxies: Dwarf - Galaxies: Evolution - Galaxies: Individual: Name: Leo A - Galaxies: Individual: Alphanumeric: GR 8 - Galaxies: Irregular

Nomenclature: Paragr. 2.1: [VSH2006] JHHMMSS.ss+DDMMSS.s N=2. Fig. 2, Table 3: [VSH2006] Leo A +XXX+YYY N=5. Fig. 3, Table 4: [VSH2006] GR 8 +XXX+YYY N=8.

Simbad objects: 73

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Number of rows : 73
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 MCG-03-01-015 G 00 01 57.9 -15 27 50   11.50 11.10 10.93   ~ 782 2
2 NGC 55 rG 00 14 53.602 -39 11 47.86 8.54 8.58 7.87 7.84   ~ 828 2
3 IC 10 rG 00 20 17.33520 +59 18 13.6480   13.6 9.5     ~ 1185 1
4 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 12317 1
5 NGC 300 GiG 00 54 53.4465638304 -37 41 03.168402396 8.83 8.69 8.13 7.46   ~ 1614 2
6 NAME Scl Group GrG 01 00 06 -33 44.2           ~ 526 0
7 IC 1613 GiC 01 04 48.4071 +02 07 10.185   10.42 10.01 9.77   ~ 1316 2
8 Z 458-20 AG? 01 07 23.0321 +16 41 00.988 15.01 14.55 14.07     ~ 148 0
9 NGC 625 AGN 01 35 04.632 -41 26 10.32 12.37 11.78 11.25 11.03 11.5 ~ 312 2
10 MCG-07-04-032 AG? 01 45 03.74 -43 35 52.9 13.45 12.92 12.63 12.51 12.8 ~ 152 1
11 SBSG 0335-052 AGN 03 37 44.06 -05 02 40.2     16.65     ~ 500 1
12 UGCA 86 AG? 03 59 48.30 +67 08 18.6   14.2 14.2     ~ 110 0
13 UGCA 92 AG? 04 32 03.8366 +63 36 51.243   16.15       ~ 128 0
14 NGC 1560 GiG 04 32 49.087 +71 52 59.20   12.1       ~ 264 0
15 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 19090 0
16 ESO 489-56 AG? 06 26 17.4435 -26 16 01.290   16.69   16.28 15.0 ~ 60 0
17 LEDA 2807061 G 07 00 29.3 -04 12 30           ~ 43 1
18 NGC 2363A HII 07 28 42.8 +69 11 21           ~ 588 3
19 NGC 2366 H2G 07 28 52.4529 +69 12 38.859 12.25 11.86 11.39 11.33   ~ 801 0
20 UGC 4305 IG 08 19 04.9864630512 +70 43 13.086910452 12.06 11.72 11.39 11.11   ~ 812 2
21 Z 311-8 GiG 08 34 07.20 +66 10 54.0 15.39 15.03 14.70 14.49   ~ 357 2
22 Z 331-51 GiG 08 37 03.00 +69 46 31.0 15.70 15.46 14.98 14.89   ~ 316 0
23 NGC 2915 AG? 09 26 11.532 -76 37 34.75 13.13 12.93 12.68 11.90 12.8 ~ 371 2
24 Mrk 116 AGN 09 34 02.1 +55 14 25           ~ 1179 1
25 Z 332-57 LSB 09 40 32.33 +71 10 56.0 14.53 14.00 13.66 13.41   ~ 372 1
26 M 81 Sy2 09 55 33.1726556496 +69 03 55.062505368   7.89 6.94     ~ 4725 3
27 [VSH2006] J095915.85+304346.1 G 09 59 15.85 +30 43 46.1           ~ 1 0
28 [VSH2006] Leo A -101-052 HII 09 59 17.2 +30 44 07           ~ 3 0
29 Z 153-10 G 09 59 26.46 +30 44 47.0 14.08 13.54 13.26 13.33   ~ 652 0
30 Z 36-12 H2G 10 00 00.8217342072 +05 20 09.533389560 12.77 12.25 11.89 11.71   ~ 569 0
31 NGC 3109 AG? 10 03 06.877 -26 09 34.46 11.10 10.42 10.04 9.91   ~ 825 2
32 MCG-01-26-030 H2G 10 11 00.5 -04 41 30 12.48 12.13 11.93 11.78   ~ 789 2
33 IC 2574 AG? 10 28 23.6148831408 +68 24 43.440012756 11.70 11.07 10.87 10.74   ~ 703 1
34 Z 351-62 bCG 11 27 59.90 +78 59 39.0   14.50       ~ 346 1
35 Z 242-46 bCG 11 33 29.12 +49 14 17.4 14.69 14.61 14.25 14.17   ~ 242 1
36 NGC 4228 SBG 12 15 39.174 +36 19 36.80 10.63 10.30 9.93 9.74   ~ 1017 1
37 NGC 4395 Sy2 12 25 48.8633109888 +33 32 48.700168152 10.84 10.54 10.11 9.98   ~ 1286 1
38 NAME CVn I dwA GiC 12 38 40.06 +32 46 00.5 16.91 16.66 16.73 16.62   ~ 242 0
39 MCG-06-28-017 AG? 12 46 00.67 -33 50 13.0   14.24   13.50 14.0 ~ 91 0
40 ACO 3526 ClG 12 48 49.2 -41 18 17           ~ 1154 2
41 NGC 4789A GiC 12 54 05.248 +27 08 58.67 14.37 14.23 13.95 13.84   ~ 614 1
42 [VSH2006] J125839.95+141425.7 G 12 58 39.95 +14 14 25.7           ~ 1 0
43 Z 71-87 H2G 12 58 40.1930636208 +14 13 00.739589628 15.24 15.16 14.98 14.81   ~ 475 0
44 MCG+08-24-090 AG? 13 13 22.839 +46 19 21.71   17       ~ 135 1
45 Z 245-36 AG? 13 14 27.997 +45 55 11.14 13.63 13.26 13.02 12.81   ~ 297 0
46 ESO 444-84 GiC 13 37 19.99 -28 02 42.0 16.04 15.34 15.05 15.05 14.9 ~ 133 1
47 Z 218-34 AG? 13 39 53.75 +40 44 25.3 15.37 14.56 14.20 14.10   ~ 165 0
48 NGC 5253 rG 13 39 55.990 -31 38 24.11 11.48 10.94 10.49 10.33 13.47 ~ 1421 4
49 NGC 5264 GiG 13 41 36.683 -29 54 47.25 13.86 12.96 12.39 12.14 15.83 ~ 164 1
50 MCG-06-30-025 EmG 13 49 17.5109711256 -36 03 48.860478360   11.00   10.11   ~ 120 1
51 NGC 5408 EmG 14 03 20.907 -41 22 39.75   12.59   11.96 12.2 ~ 368 3
52 Z 133-19 AG? 14 15 57.0834 +23 03 29.871 15.40 14.77 14.41 14.32   ~ 296 0
53 Z 247-26 AG? 14 24 43.21 +44 31 41.8 14.24 13.54 13.17 13.07   ~ 217 0
54 IC 4662 bCG 17 47 09.192 -64 38 19.25   11.75 11.1 10.45   ~ 253 4
55 NAME Sgr dIG G 19 29 59.0 -17 40 41   15.5 13.6     ~ 323 1
56 NGC 6822 G 19 44 56.199 -14 47 51.29   18 8.1     ~ 1661 0
57 MCG-02-53-003 G 20 46 51.7 -12 50 54 15.75 15.18 14.83 14.46   ~ 470 1
58 IC 5152 rG 22 02 41.521 -51 17 47.20   11.03 10.9 10.19   ~ 273 1
59 Z 431-72 G 23 28 35.2 +14 44 35 13.85 13.16 12.52     ~ 499 1
60 MCG-05-56-001 G 23 43 45.549 -31 57 24.37 14.55 14.03 13.73 13.63   ~ 162 1
61 [VSH2006] GR 8 +019-019 HII ~ ~           ~ 3 0
62 [VSH2006] GR 8 -012-022 HII ~ ~           ~ 2 0
63 [VSH2006] GR 8 -013-032 ? ~ ~           ~ 2 0
64 [VSH2006] GR 8 +008-011 HII ~ ~           ~ 3 0
65 [VSH2006] GR 8 -002-012 HII ~ ~           ~ 2 0
66 [VSH2006] Leo A +089+031 HII ~ ~           ~ 1 0
67 [VSH2006] Leo A +069-018 HII ~ ~           ~ 3 0
68 [VSH2006] Leo A -091-048 HII ~ ~           ~ 2 0
69 NAME Local Group GrG ~ ~           ~ 9325 0
70 [VSH2006] GR 8 +004-006 HII ~ ~           ~ 2 0
71 [VSH2006] GR 8 +001-008 HII ~ ~           ~ 2 0
72 [VSH2006] Leo A +112-020 HII ~ ~           ~ 2 0
73 [VSH2006] GR 8 +001+027 HII ~ ~           ~ 2 0

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