scholarly journals VLT/FORS Surveys of Wolf-Rayet Stars in the Nearby Universe

2007 ◽  
Vol 3 (S250) ◽  
pp. 327-332
Author(s):  
Lucy J. Hadfield ◽  
Paul A. Crowther
Keyword(s):  
Local Group ◽  
Narrow Band ◽  
Dwarf Galaxy ◽  
Narrow Band Imaging ◽  
Interstellar Extinction ◽  
Spectroscopic Studies ◽  
Order Of Magnitude ◽  
Low Metallicity ◽  
Massive Clusters ◽  
Blue Compact Dwarf Galaxy

AbstractWe present results from a series of VLT/FORS narrow-band imaging and spectroscopic surveys of Wolf-Rayet (WR) stars in nearby spiral galaxies and compare observed populations in high- and low metallicity environments. The metal-rich galaxy M 83 is seen to host an exceptional WR content, with over 1000 WR stars being detected. N(WC)/N(WN) ~ 1.2 and late-type WC subtypes dominate the WC population. At low metallicity, ~100 stars has been identified within NGC 1313, with N(WC)/N(WN) ~ 0.5. In contrast to M83, the WC population of NGC 1313 comprises solely early subtypes plus a WO star (the first WO star to be identified beyond the Local Group). Consequently, the dominant WC subtype may serve as a crude metallicity diagnostic for WR galaxies.In addition, the WR content of the blue compact dwarf galaxy NGC 3125 is examined. Previous UV and optical spectroscopic studies of knot A in NGC 3125 derive WR populations which differ by more than an order of magnitude. New VLT observations and archival HST spectroscopy reconcile this discrepancy via the use of LMC WR spectral templates and a reduced nebular-derived interstellar extinction. Empirical N(WR)/N(O) ratios for clusters within NGC 3125 are a factor of two higher than evolutionary synthesis predictions but are consistent with those observed for other young massive clusters.

scholarly journals Wolf-Rayet stars at 1 - 2 Mpc

2003 ◽  
Vol 212 ◽  
pp. 547-548 ◽  
Author(s):  
Paul A. Crowther ◽  
Jay B. Abbott ◽  
Laurent Drissen ◽  
Hansrüdi Schild ◽  
Werner Schmutz ◽  
...  
Keyword(s):  
Optical Spectroscopy ◽  
Spiral Galaxy ◽  
Local Group ◽  
Narrow Band ◽  
Dwarf Galaxy ◽  
Narrow Band Imaging ◽  
Ic 10

We present new narrow-band imaging and optical spectroscopy of Wolf-Rayet stars in the Local Group dwarf galaxy IC 10 (Gemini-N- gmos) and Sculptor group spiral galaxy NGC 300 (VLT fors2).

scholarly journals Haro15: Is it actually a low metallicity galaxy?

2009 ◽  
Vol 5 (S265) ◽  
pp. 243-244
Author(s):  
Verónica Firpo ◽  
Guillermo Bosch ◽  
Guillermo Hägele ◽  
Ángeles I. Díaz ◽  
Nidia Morrell
Keyword(s):  
Dwarf Galaxy ◽  
Empirical Methods ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Ionization Structure ◽  
The Galaxy ◽  
Low Metallicity ◽  
Echelle Spectroscopy ◽  
Abundance Determination ◽  
Blue Compact Dwarf Galaxy

AbstractWe present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the η and η' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions.

scholarly journals Multiwavelength Observations of the Low-Metallicity Blue Compact Dwarf Galaxy SBS 0335−052

2001 ◽  
Vol 122 (4) ◽  
pp. 1736-1746 ◽  
Author(s):  
Daniel A. Dale ◽  
George Helou ◽  
Gerry Neugebauer ◽  
B. T. Soifer ◽  
David T. Frayer ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Low Metallicity ◽  
Blue Compact Dwarf Galaxy ◽  
Multiwavelength Observations

scholarly journals Wolf-Rayet Stars in M31

1986 ◽  
Vol 116 ◽  
pp. 231-232
Author(s):  
M.M. Shara ◽  
A.F.J. Moffat
Keyword(s):  
Narrow Band ◽  
Narrow Band Imaging ◽  
Imaging Techniques ◽  
Hii Regions ◽  
Interstellar Extinction ◽  
Limiting Factor ◽  
Main Body ◽  
Weak Line ◽  
The Mean ◽  
Line Equivalent Width

We have completed a survey of the closest giant spiral galaxy beyond our own for Wolf-Rayet stars, using narrow band imaging techniques (cf. Moffat and Shara 1983, Ap. J., 273, 544). About 90% of the main body of M31 has been thoroughly searched to B ≅ 21.5 (MB ≅ −3.5) to a level of emission line equivalent width We(HeII 4686 A) ≳ 60 A. We do not expect interstellar extinction to be a limiting factor in the detection of WR stars, except possibly in the localized neighborhoods of massive HII regions. The mean extinction for stars in the disk is estimated to be AB ≲ 0.9 mag. Although some weak-line WN stars will have escaped detection, the survey should be complete for WC stars.

scholarly journals Comparative Morphology of the HST Color-Magnitude Diagram of the Nearby Blue Compact Dwarf Galaxy VII Zw 403 with that of Local Group Dwarfs

1999 ◽  
Vol 192 ◽  
pp. 464-468
Author(s):  
R.E. Schulte-Ladbeck ◽  
U. Hopp ◽  
M. M. Crone
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Comparative Morphology ◽  
Star Formation History ◽  
Stellar Content ◽  
Halo Structure ◽  
Formation History ◽  
Magnitude Diagram ◽  
Blue Compact Dwarf Galaxy

There are no examples of Blue Compact Dwarf (BCD) galaxies known within the Local Group (LG). Multicolor HST/WFPC2 observations of the nearby BCD VII Zw 403 (= UGC 6456) now resolve single stars with the quality (in terms of limiting magnitude and completeness) previously achieved for LG dwarfs from the ground. We use the MI, V - I color-magnitude diagrams (CMDs) of several LG dwarfs as templates to assess the stellar content and star-formation history (SFH) of the BCD VII Zw 403. This is the first BCD for which a clear spatial segregation of the resolved stellar content into a “core-halo” structure is detected: active star formation is observed in the central region of VII Zw 403, while in “Baade's red sheet”, this young population is strikingly absent. If BCD halos are home to dominant ancient stellar populations, then the fossil record conflicts with delayed-format ion scenarios for dwarfs. We present a sketch of the SFH in the core and halo of VII Zw 403.

scholarly journals [TSUP]12[/TSUP]CO Mapping of the Low-Metallicity Blue Compact Dwarf Galaxy Markarian 86

2002 ◽  
Vol 573 (2) ◽  
pp. L101-L105 ◽  
Author(s):  
A. Gil de Paz ◽  
S. A. Silich ◽  
B. F. Madore ◽  
C. Sánchez Contreras ◽  
J. Zamorano ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Low Metallicity ◽  
Blue Compact Dwarf Galaxy

scholarly journals Lithium and beryllium in the Gaia-Enceladus galaxy

2020 ◽  
Vol 496 (3) ◽  
pp. 2902-2909
Author(s):  
P Molaro ◽  
G Cescutti ◽  
X Fu
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Chemical Abundances ◽  
Dwarf Stars ◽  
Evolution Experiment ◽  
External Galaxies ◽  
Low Metallicity ◽  
Gaia Dr2

ABSTRACT Data from Gaia DR2 and The Apache Point Observatory Galactic Evolution Experiment surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyr ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on 7Li and 9Be in dwarf stars that are out of reach even in Local Group galaxies. Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The 7Li abundances of stars at the low metallicity end overlap with those of the Galactic halo. These are effective extragalactic 7Li measurements, which suggest that the 7Li Spite plateau is universal, as is the cosmological 7Li problem. We found a 7Li-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect 9Be abundance for a subsample of 25 Gaia-Enceladus stars from literature. Their abundances share the Galactic [Be/H] values at the low metallicity end but grow slower with [Fe/H] and show a reduced dispersion. This suggests that the scatter observed in the Milky Way could reflect the different 9Be evolution patterns of different stellar components that are mixed-up in the Galactic halo.

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