J/A+A/627/A34 GC hot UV-bright stars model spectra (Moehler+, 2019)
Hot UV-bright stars of galactic globular clusters.
Moehler S., Landsman W.B., Lanz T., Miller Bertolami M.M.
<Astron. Astrophys. 627, A34 (2019)>
=2019A&A...627A..34M 2019A&A...627A..34M (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Clusters, globular; Populations, stellar ; Ultraviolet ;
Spectroscopy
Keywords: stars: AGB and post-AGB - globular clusters: general
Abstract:
We have performed a census of the UV-bright population in 78 globular
clusters using wide-field UV telescopes. This population includes a
variety of phases of post-horizontal branch (HB) evolution, including
hot post-asymptotic giant branch (AGB) stars, and post-early AGB
stars. There are indications that old stellar systems like globular
clusters produce fewer post-(early) AGB stars than currently predicted
by evolutionary models, but observations are still scarce. We wish to
derive effective temperatures, surface gravities, and helium
abundances of the luminous hot UV-bright stars in these clusters to
determine their evolutionary status and compare the observed numbers
to predictions from evolutionary theory. We obtained FORS2
spectroscopy of 11 of these UV-selected objects (covering a range of
-2.3<[Fe/H]←1.0), which we (re-)analysed together with previously
observed data. We used model atmospheres of different metallicities,
including super-solar ones. Where possible, we verified our
atmospheric parameters using UV spectrophotometry and searched for
metal lines in the optical spectra. We calculated evolutionary
sequences for four metallicity regimes and used them together with
information about the HB morphology of the globular clusters to
estimate the expected numbers of post-AGB stars. We find that
metal-rich model spectra are required to analyse stars hotter than
40000 K. Seven of the eleven new luminous UV-bright stars are post-AGB
or post-early AGB stars, two are evolving away from the HB, one is a
foreground white dwarf, and another is a white dwarf merger. Taking
into account published information on other hot UV-bright stars in
globular clusters, we find that the number of observed hot post-AGB
stars generally agrees with the predicted values, although the numbers
are still low. Spectroscopy is clearly required to identify the
evolutionary status of hot UV-bright stars. For hotter stars,
metal-rich model spectra are required to reproduce their optical and
UV spectra, which may affect the flux contribution of hot post-AGB
stars to the UV spectra of evolved populations. Adding published
information on other hot UV-bright stars in globular clusters, we find
that the number of observed hot post-AGB stars generally agrees with
the predicted values, although the numbers are still low.
Description:
Optical medium- and low-resolution spectra (flux-calibrated and
normalized) of 13 UV bright stars in globular clusters are presented
together with the atmospheric parameters derived from them. The
following globular clusters have been observed: NGC5139, NGC6121,
NGC6656, NGC6712, NGC6779, NGC7099. The flux-calibrated spectra were
corrected to laboratory wavelengths and their continua were
normalized. Effective temperatures, surface gravities, and helium
abundances were derived from line profile fits and the corresponding
best-fitting model spectra are also presented here. We also present
post-helium core burning evolutionary sequences calculated low mass
stars for [M/H] = -2.3, -2.0, -1.5, -1.0.
Grid of post-horizontal branch evolutionary sequences for four
different metallicities. Models at the Zero Age Horizontal Branch
(ZAHB) were constructing by removing mass at the tip of the Red Giant
Branch (RGB). Details about the initial model on the main sequence are
provided in table B.1 of the article. Each file contains all the
sequences with a given initial metallicity and are named as
CDSFeH-1.0.dat, CDSFeH-1.5.dat, CDSFeH-2.0.dat, and
CDSFeH-2.3.dat (corresponding to metallicities [Fe/H]=-1, -1.5, -2,
-2.3, see Table 8 of the Article)
All sequences are presented at similar timesteps
Sequences are presented until their luminosity drops to 10 solar
luminosities.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
stars.dat 129 20 List of stars with atmospheric parameters and
evolutionary status
efosc2-n.dat 32 2565 Normalized EFOSC2 spectra
fors2-n.dat 164 1857 Normalized FORS2 spectra
fors2-f.dat 164 1857 Flux-calibrated FORS2 spectra
lte.dat 125 1295 Best-fitting LTE model spectra
nlte.dat 138 12296 Best-fitting NLTE model spectra
wdmodel.dat 20 2468 Best-fitting metal-free NLTE model spectrum
for NGC7099-UVBS2
feh-10.dat 77 17949 *Evolutionary properties of 5 post-AGB models
with initial metallicity [M/H]=-1.0 (Tab. B.1)
feh-15.dat 77 14518 *Evolutionary properties of 5 post-AGB models
with initial metallicity [M/H]=-1.5 (Tab. B.1)
feh-20.dat 77 9832 *Evolutionary properties of 5 post-AGB models
with initial metallicity [M/H]=-2.0 (Tab. B.1)
feh-23.dat 77 10637 *Evolutionary properties of 5 post-AGB models
with initial metallicity [M/H]=-2.3 (Tab. B.1)
--------------------------------------------------------------------------------
Note on feh*.dat: Inside each file each sequence is started with a short header
(2 lines) indicating the nature of the model (post-ZAHB), and the ZAHB mass.
Different evolutionary sequences are separated by 2 empty lines.
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Byte-by-byte Description of file: stars.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Cluster Globular cluster name
9- 15 A7 --- Star Star name
17- 18 I2 h RAh Right Ascension (J2000)
20- 21 I2 min RAm Right Ascension (J2000)
23- 27 F5.2 s RAs Right Ascension (J2000)
29 A1 --- DE- Declination sign (J2000)
30- 31 I2 deg DEd Declination (J2000)
33- 34 I2 arcmin DEm Declination (J2000)
36- 39 F4.1 arcsec DEs Declination (J2000)
41- 45 I5 K Teff Effective temperature
47- 50 F4.2 [cm/s2] logg logarithmic surface gravity
52- 56 F5.2 [-] logHe/H logarithmic helium abundance by particle
number relative to hydrogen
58- 62 A5 --- Status Evolutionary status
64- 75 A12 --- EFOSC2-N Name of the column with fluxes in
efosc2-n.dat table
77- 88 A12 --- FORS2 Name of the column with fluxes in
fors2-n.dat and fors2-f.dat tables
90- 101 A12 --- LTE Name of the column with fluxes in
lte.dat table
103-114 A12 --- NLTE Name of the column with fluxes in
nlte.dat table
119-129 A11 --- WDmodel Name of the column with fluxes in
wdmodel.dat table
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Byte-by-byte Description of file: efosc2-n.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 8 F7.3 nm lambda Wavelength
10- 20 E11.5 --- OCen-ROA542 ?=0 Normalized spectrum for NGC5139-ROA542
22- 32 E11.5 --- OCen-ROA3596 ?=0 Normalized spectrum for NGC5139-ROA3596
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fors2-n.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 8 F7.3 nm lambda Wavelength
10- 21 E12.6 --- OCen-UIT151 ?=0 Normalized spectrum for NGC5139-UIT151
23- 34 E12.6 --- OCen-UIT644 ?=0 Normalized spectrum for NGC5139-UIT644
36- 47 E12.6 --- OCen-UIT1275 ?=0 Normalized spectrum for NGC5139-UIT1275
49- 60 E12.6 --- OCen-UIT1425 ?=0 Normalized spectrum for NGC5139-UIT1425
62- 73 E12.6 --- OCen-Dk3873 ?=0 Normalized spectrum for NGC5139-Dk3873
75- 86 E12.6 --- OCen-ROA5342 ?=0 Normalized spectrum for NGC5139-ROA5342
88- 99 E12.6 --- NGC6121-U2 ?=0 Normalized spectrum for NGC6121-UVBS2
101-112 E12.6 --- NGC6656-U1n ?=0 Normalized spectrum for NGC6656-UVBS2
(narrow extraction)
114-125 E12.6 --- NGC6656-U1c ?=0 Normalized spectrum for NGC6656-UVBS2
(companion corrected)
127-138 E12.6 --- NGC6712-C49 ?=0 Normalized spectrum for NGC6712-C49
140-151 E12.6 --- NGC6779-ZNG2 ?=0 Normalized spectrum for NGC6779-ZNG2
153-164 E12.6 --- NGC7099-U2 ?=0 Normalized spectrum for NGC7099-UVBS2
--------------------------------------------------------------------------------
Byte-by-byte Description of file: fors2-f.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 nm lambda Wavelength
10- 21 E12.6 10mW/m2/nm OCen-UIT151 ?=0 Flux-calibrated spectrum for
NGC5139-UIT151
23- 34 E12.6 10mW/m2/nm OCen-UIT644 ?=0 Flux-calibrated spectrum for
NGC5139-UIT644
36- 47 E12.6 10mW/m2/nm OCen-UIT1275 ?=0 Flux-calibrated spectrum for
NGC5139-UIT1275
49- 60 E12.6 10mW/m2/nm OCen-UIT1425 ?=0 Flux-calibrated spectrum for
NGC5139-UIT1425
62- 73 E12.6 10mW/m2/nm OCen-Dk3873 ?=0 Flux-calibrated spectrum for
NGC5139-Dk3873
75- 86 E12.6 10mW/m2/nm OCen-ROA5342 ?=0 Flux-calibrated spectrum for
NGC5139-ROA5342
88- 99 E12.6 10mW/m2/nm NGC6121-U2 ?=0 Flux-calibrated spectrum for
NGC6121-UVBS2
101-112 E12.6 10mW/m2/nm NGC6656-U1n ?=0 Flux-calibrated spectrum for
NGC6656-UVBS2 (narrow extraction)
114-125 E12.6 10mW/m2/nm NGC6656-U1c ?=0 Flux-calibrated spectrum for
NGC6656-UVBS2 (companion corrected)
127-138 E12.6 10mW/m2/nm NGC6712-C49 ?=0 Flux-calibrated spectrum for
NGC6712-C49
140-151 E12.6 10mW/m2/nm NGC6779-ZNG2 ?=0 Flux-calibrated spectrum for
NGC6779-ZNG2
153-164 E12.6 10mW/m2/nm NGC7099-U2 ?=0 Flux-calibrated spectrum for
NGC7099-UVBS2
--------------------------------------------------------------------------------
Byte-by-byte Description of file: lte.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 8 F7.3 nm lambda Wavelength
10- 21 E12.6 --- N2808-C2946 ?=0 Metal-poor best fit LTE model spectrum
for NGC2808-C2946
23- 34 E12.6 --- N2808-C2947 ?=0 Metal-poor best fit LTE model spectrum
for NGC2808-C2947
36- 47 E12.6 --- N2808-C4594 ?=0 Metal-poor best fit LTE model spectrum
for NGC2808-C4594
49- 60 E12.6 --- OCen-ROA542 ?=0 Metal-poor best fit LTE model spectrum
for NGC5139-ROA542
62- 73 E12.6 --- OCen-ROA3596 ?=0 Metal-rich best fit LTE model spectrum
for NGC5139-ROA3596
75- 86 E12.6 --- OCen-UIT1275 ?=0 Metal-rich best fit LTE model spectrum
for NGC5139-UIT1275
88- 99 E12.6 --- OCen-UIT1425 ?=0 Metal-rich best fit LTE model spectrum
for NGC5139-UIT1425
101-112 E12.6 --- N6723-IV9 ?=0 Metal-poor best fit LTE model spectrum
for NGC6723-IV9
114-125 E12.6 --- N6752-B2004 ?=0 Metal-poor best fit LTE model spectrum
for NGC6752-B2004
--------------------------------------------------------------------------------
Byte-by-byte Description of file: nlte.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 8 F7.3 nm lambda Wavelength
10- 21 E12.6 --- OCen-UIT151 ?=0 Metal-rich best fit NLTE model
spectrum for NGC5139-UIT151
23- 34 E12.6 --- OCen-UIT644 ?=0 Metal-poor best fit NLTE model
spectrum for NGC5139-UIT644
36- 47 E12.6 --- OCen-Dk3873 ?=0 Metal-rich best fit NLTE model
spectrum for NGC5139-Dk3873
49- 60 E12.6 --- OCen-ROA5342 ?=0 Metal-rich best fit NLTE model
spectrum for NGC5139-ROA5342
62- 73 E12.6 --- N6121-Y453 ?=0 Metal-rich best fit NLTE model
spectrum for NGC6121-Y453
75- 86 E12.6 --- N6121-UVBS2 ?=0 Metal-rich best fit NLTE model
spectrum for NGC6121-UVBS2
88- 99 E12.6 --- N6656-UVBS2n ?=0 Metal-rich best fit NLTE model
spectrum for NGC6656-UVBS2
101-112 E12.6 --- N6712-C49 ?=0 Metal-rich best fit NLTE model
spectrum for NGC6712-C49
114-125 E12.6 --- N6723-III60 ?=0 Metal-rich best fit NLTE model
spectrum for NGC6723-III60
127-138 E12.6 --- N6779-ZNG2 ?=0 Metal-poor best fit NLTE model
spectrum for NGC6779-ZNG2
--------------------------------------------------------------------------------
Byte-by-byte Description of file: wdmodel.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 8 F7.3 nm lambda Wavelength
11- 20 F10.8 --- N7099-UVBS2 ?=0 Metal-free best fit NLTE model spectrum
for NGC7099-UVBS2
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): feh*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 E12.6 Myr t age in years since the ZAHB
14- 25 E12.6 [Lsun] LogL logarithm of the stellar luminosity
27- 38 E12.6 [K] LogTeff logarithm of the effective temperature
40- 51 E12.6 [cm/s2] Logg logarithm of the surface gravity
53- 64 E12.6 Msun Mstar total mass of the star
66- 77 E12.6 Msun/yr mdM/dt Logarithm of the Mass Loss Rate (-dM/dt)
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Acknowledgements:
Sabine Moehler, smoehler(at)eso.org
Marcelo Miller-Bertolami, mmiller(at)fcaglp.unlp.edu.ar
(End) Patricia Vannier [CDS] 24-May-2019