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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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
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
Byte-by-byte Description of file: table[34].dat
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)
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.
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 31-May-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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