J/A+A/526/A136 Hot HB stars in ω Cen (Moehler+, 2011)
The hot horizontal-branch stars in ω Centauri.
Moehler S., Dreizler S., Lanz T., Bono G., Sweigart A.V., Calamida A.,
Nonino M.
<Astron. Astrophys., 526, A136 (2011)>
=2011A&A...526A.136M 2011A&A...526A.136M
ADC_Keywords: Clusters, globular ; Stars, horizontal branch ; Blue objects ;
Radial velocities ; Effective temperatures
Keywords: stars: horizontal-branch - stars: evolution -
techniques: spectroscopic - globular clusters: individual: NGC 5139
Abstract:
UV observations of some massive globular clusters have revealed a
significant population of stars hotter and fainter than the hot end of
the horizontal branch (HB), the so-called blue hook stars. This
feature might be explained either by the late hot flasher scenario
where stars experience the helium flash while on the white dwarf
cooling curve or by the progeny of the helium-enriched sub-population
postulated to exist in some clusters. Previous spectroscopic analyses
of blue hook stars in omega Cen and NGC 2808 support the late hot
flasher scenario, but the stars contain much less helium than expected
and the predicted C and N enrichment cannot be verified.
We compare the observed effective temperatures, surface gravities,
helium abundances, and carbon line strengths (where detectable) of our
targets stars with the predictions of the two aforementioned
scenarios.
Description:
Moderately high resolution spectra of hot HB stars in the globular
cluster omega Cen were analysed for radial velocity variations,
atmospheric parameters, and abundances using LTE and non-LTE model
atmospheres.
The spectroscopic data were obtained in 2005 (4 observations) and in
2006 (5 observations) in Service Mode using the MEDUSA mode of the
multi-object fiber spectrograph FLAMES + GIRAFFE on the UT2 Telescope
of the VLT. We used the low spectroscopic resolution mode with the
spectral range 3964Å-4567Å (LR2, R=6400) and observed spectra
for a total of 109 blue hook and canonical blue HB/EHB star candidates
(see Table 1) and for 17 sky background positions. Each observation
had an exposure time of 2550s to keep the total execution time of the
observing block shorter than one hour.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 44 109 Target coordinates, heliocentric radial
velocities, and B brightness
table3.dat 45 66 Atmospheric parameters for stars with sub-solar
helium abundances
table4.dat 45 36 Atmospheric parameters for stars with super-solar
helium abundances as derived with TLUSTY atmospheres
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See also:
J/ApJ/663/1021 : Log of ω Cen scientific images (Castellani+, 2007)
J/MNRAS/399/195 : Blue & red spectra of ω Cen HB stars (Van Loon+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- Seq Sequential number (<[MDL2011] NNNNNN> in Simbad)
8 I1 --- n_Seq [1/4]? Note on target star (1)
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 19 F4.1 s RAs Right ascension (J2000)
21 A1 --- DE- Declination sign (J2000)
22- 23 I2 deg DEd Declination (J2000)
25- 26 I2 arcmin DEm Declination (J2000)
28- 31 F4.1 arcsec DEs Declination (J2000)
33- 38 F6.3 mag Bmag B magnitude
40- 44 F5.1 km/s HRV ?=- Heliocentric radial velocity
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Note (1): Notes as follows:
1 = Very noisy spectra
2 = only 2 spectra extracted
3 = no spectra extracted
4 = G-band and/or FeI 4325Å visible
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Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- Seq Sequential number
7 A1 --- n_Seq [C] dedicated model atmosphere (1)
9- 13 F5.3 --- chi2 chi2 value
15- 19 I5 K Teff Effective temperature
21- 24 I4 K e_Teff rms uncertainty on Teff
26- 29 F4.2 [cm/s2] logg Surface gravity
31- 34 F4.2 [cm/s2] e_logg rms uncertainty on logg
36- 40 F5.2 [---] log(He/H) He/H number density ratio
42- 45 F4.2 [---] e_log(He/H) rms uncertainty on log(He/H)
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Note (1): C indicates the use of C/N enhanced model atmospheres, whereas no
notation indicates the use of model atmospheres using the cluster metallicity.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 31-May-2011