2006AJ....131.2256Y


C.D.S. - SIMBAD4 rel 1.7 - 2021.05.06CEST01:20:52

2006AJ....131.2256Y - Astron. J., 131, 2256-2273 (2006/April-0)

Elemental abundance ratios in stars of the outer galactic disk. III. Cepheids.

YONG D., CARNEY B.W., DE ALMEIDA M.L.T. and POHL B.L.

Abstract (from CDS):

We present metallicities, [Fe/H], and elemental abundance ratios, [X/Fe], for a sample of 24 Cepheids in the outer Galactic disk based on high-resolution echelle spectra. The sample members have galactocentric distances covering 12 kpc≤RGC≤17.2 kpc, making them the most distant Galactic Cepheids upon which detailed abundance analyses have been performed. We find subsolar ratios of [Fe/H] and overabundances of [α/Fe], [La/Fe], and [Eu/Fe] in the program stars. All abundance ratios exhibit a dispersion that exceeds the measurement uncertainties. As seen in our previous studies of old open clusters and field giants, enhanced ratios of [α/Fe] and [Eu/Fe] reveal that recent star formation has taken place in the outer disk with Type II supernovae preferentially contributing ejecta to the interstellar medium and with Type Ia supernovae playing only a minor role. The enhancements for La suggest that asymptotic giant branch stars have contributed to the chemical evolution of the outer Galactic disk. Some of the young Cepheids are more metal-poor than the older open clusters and field stars at comparable galactocentric distances. This demonstrates that the outer disk is not the end result of the isolated evolution of an ensemble of gas and stars. We showed previously that the older open clusters and field stars reached a basement metallicity at about 10-11 kpc. The younger Cepheids reach the same metallicity but at larger galactocentric distances, roughly 14 kpc. This suggests that the Galactic disk has been growing with time, as predicted from numerical simulations. The outer disk Cepheids appear to exhibit a bimodal distribution for [Fe/H] and [α/Fe]. Most of the Cepheids continue the trends with galactocentric distance exhibited by S. M. Andrievsky's larger Cepheid sample, and we refer to these stars as the ``Galactic Cepheids.'' A minority of the Cepheids show considerably lower [Fe/H] and higher [α/Fe], and we refer to these stars as the ``Merger Cepheids.'' One signature of a merger event would be composition differences between the Galactic and Merger Cepheids. The Cepheids satisfy this requirement, and we speculate that the distinct compositions suggest that the Merger Cepheids may have formed under the influence of significant merger or accretion events. The short lifetimes of the Cepheids reveal that the merger event may be ongoing, with the Monoceros Ring and Canis Major galaxy being possible merger candidates.

Abstract Copyright:

Journal keyword(s): Galaxy: Abundances - Galaxy: Disk

Simbad objects: 40

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Number of rows : 40

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 V* FO Cas cC* 00 17 02.5025198024 +60 48 10.101461315   15.67 14.00     ~ 24 0
2 V* NY Cas cC* 00 40 23.1965486106 +58 37 06.678600614           ~ 32 0
3 V* IO Cas cC* 01 47 02.7158901133 +59 36 22.527290973   14.84       ~ 29 0
4 V* CI Per cC* 02 05 02.1930515775 +57 08 34.562804941           ~ 30 0
5 V* GP Per Ce* 04 23 19.1737333013 +44 14 12.740209377   13.40 14.20     ~ 20 0
6 V* SZ Tau cC* 04 37 14.7778803229 +18 32 34.929341041 7.65 7.13 6.37     F6.7:Ib 292 0
7 V* OT Per cC* 04 38 37.9378681324 +47 44 25.008084048   15.71 13.47     ~ 36 0
8 V* HQ Per cC* 04 43 57.8806998785 +40 50 05.207699721           F 35 0
9 V* EW Aur cC* 04 51 24.8479090059 +38 11 18.786536871   14.60       ~ 40 0
10 V* CY Aur cC* 04 57 40.0807277112 +46 05 33.112390660   13.44 12.04     ~ 48 0
11 V* RX Aur cC* 05 01 23.1881737714 +39 57 37.422344258   8.49 7.62   6.594 G0III 197 0
12 V* ER Aur cC* 05 13 09.9827679367 +41 59 25.889070826   12.65 11.63 11.040   ~ 41 0
13 V* YZ Aur cC* 05 15 21.9827122069 +40 04 40.883139360   11.77 10.24     G5 96 0
14 V* IN Aur cC* 05 15 27.1853724564 +37 22 20.865027638   15.28       ~ 21 0
15 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15333 1
16 V* GV Aur cC* 05 44 14.0002147362 +37 35 12.735789058           ~ 28 0
17 V* CR Ori cC* 06 05 44.7233260757 +13 14 23.957029410   12.97     10.931 F7 45 0
18 V* T Mon cC* 06 25 12.9997562821 +07 05 08.561189768 8.24 7.20 5.98   4.996 G3Iabv+A0p 450 1
19 V* V484 Mon cC* 06 31 05.4422248659 -02 08 48.456914326     13.67   12.306 ~ 27 0
20 V* CU Mon cC* 06 32 46.7955605374 +00 02 35.316926303   15.02     11.923 ~ 44 0
21 V* WW Mon cC* 06 33 37.1817036531 +09 12 12.840769070   13.65 12.492   11.155 F6 57 0
22 V* EE Mon cC* 06 50 48.6826876756 -07 58 50.632391554   14.03 13.06   11.724 ~ 42 0
23 V* XZ CMa cC* 07 00 24.8328224100 -20 25 54.131989035     13.01     ~ 26 0
24 * zet Gem cC* 07 04 06.5307903 +20 34 13.073871 5.20 4.58 3.79   3.082 G1Ib 541 0
25 V* FI Mon cC* 07 10 37.9924208299 -07 07 22.461492125   14.07 12.900   11.578 ~ 43 0
26 NAME CMa Dwarf Galaxy G 07 12.6 -27 40     -0.1     ~ 194 1
27 V* HW Pup cC* 07 57 42.1676771396 -27 36 06.840883085   13.35 12.018   10.51 ~ 48 0
28 V* NT Pup cC* 07 58 46.3396293858 -38 59 39.657439618   11.0     10.769 ~ 25 0
29 V* CE Pup cC* 08 14 08.0391488919 -42 34 05.358820198     11.68     ~ 33 0
30 NGC 2682 OpC 08 51 18 +11 48.0           ~ 2096 0
31 V* HQ Car cC* 10 20 31.9898303153 -61 14 57.414334235   12.50 11.7   11.292 ~ 29 0
32 * alf Boo RG* 14 15 39.67207 +19 10 56.6730 2.46 1.18 -0.05 -1.03 -1.68 K1.5IIIFe-0.5 2170 0
33 V* U Sgr cC* 18 31 53.3321808602 -19 07 30.262730218 8.50 7.81 6.68   5.413 G1Ib 439 0
34 V* SV Vul cC* 19 51 30.9059608126 +27 27 36.835645654 8.65 7.86 6.74   5.703 F8Ia 404 0
35 * eta Aql cC* 19 52 28.3677478 +01 00 20.369619 5.12 4.61 3.80   3.030 F6Iab+B9.8V 642 0
36 * 10 Sge cC* 19 56 01.2614273274 +16 38 05.236276391 6.45 6.03 5.36 6.81 4.789 F7Ib 332 0
37 V* X Cyg cC* 20 43 24.1918662954 +35 35 16.075732392 8.69 7.70 6.47   5.241 F7Ib 444 0
38 V* T Vul cC* 20 51 28.2382502598 +28 15 01.816605372 6.89 6.49 5.77   5.061 F5Ib+A0.8V 324 0
39 * del Cep cC* 22 29 10.2650184 +58 24 54.713856 4.71 4.35 3.75   3.219 F5Iab:+B7-8 689 0
40 NAME Monoceros Stream St* ~ ~           ~ 327 0

    Equat.    Gal    SGal    Ecl

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2021.05.06-01:20:52

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