J/A+A/693/A136 Spectra of HB stars in 3 globular clusters (Moehler, 2025)
Pollution versus diffusion: Abundance patterns of blue horizontal branch stars
in the globular clusters NGC 6388, NGC 6397, and NGC 6752.
Moehler S.
<Astron. Astrophys. 693, A136 (2025)>
=2025A&A...693A.136M 2025A&A...693A.136M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, horizontal branch ; Abundances
Keywords: stars: abundances - stars: horizontal branch -
globular clusters: individual: NGC 6397 -
globular clusters: individual: NGC 6752 -
globular clusters: individual: NGC 6388
Abstract:
The metal-rich ([M/H]=-0.48) bulge globular cluster NGC 6388 displays
a blue horizontal branch (HB). Helium enrichment, which is correlated
with changes seen among other light elements, might explain this
feature. Conversely, the hot HB stars in the metal-poor globular
clusters NGC 6397 and NGC 6752 display high abundances of heavy
elements caused by radiative levitation. I want to determine the
abundances of cool blue HB stars in NGC 6388 to verify whether they
are helium-enriched. To exclude the effects of radiative levitation
for NGC 6388 and to investigate the abundance changes caused by
radiative levitation, I analysed the blue HB stars in NGC 6397
and NGC 6752.
I obtained high-resolution spectra for all three clusters. I then
determined the effective temperatures and surface gravities from
UV-optical photometry (NGC 6388) and the spectra (NGC 6397, NGC 6752)
together with local thermodynamic equilibrium (LTE) model spectra. The
results were used together with equivalent widths by the GALA program,
which provides consistent atmospheric parameters and abundances.
For NGC 6397 and NGC 6752, only moderately hot HB stars were suitable
for analysis with GALA. When including the literature data, a large
scatter is seen at the onset of radiative levitation, followed by
increasing abundances up to about 13500K (Si, Fe), then turning to a
plateau (Si) and a forking (Fe) for higher temperatures. In NGC 6388,
the star 4113 shows variations in radial velocity, which may indicate
binarity. For the remaining three blue HB stars, the metal abundances
are consistent with the products of hot hydrogen burning. The data
were too noisy to allow for the helium abundances to be measured.
The presence of hot hydrogen burning products in the blue HB stars in
NGC 6388 could indicate helium enrichment. The abundance variations
with temperature in moderately hot HB stars in NGC 6397 and NGC 6752
suggest an influence of parameters beyond rotation and effective
temperature.
Description:
High resolution spectra of blue horizontal branch stars in the
globular clusters in NC6388, NGC6397, and NGC6752 are presented here,
together with the equivalent width measurements and information on the
lines used for their analysis. The flux calibration is not an absolute
one, because the spectra were observed with narrow slits, which caused
flux losses.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 193 32 List of all observed stars with coordinates
from Gaia
ngc6388d.dat 88 1841 Equivalent widths and line parameters for the
stars in NGC6388
ngc6397d.dat 88 1185 Equivalent widths and line parameters for the
stars in NGC6397
ngc6752l.dat 88 1493 Equivalent widths and line parameters for the
stars in NGC6752 observed in 2000
ngc6752d.dat 88 1485 Equivalent widths and line parameters for the
stars in NGC6752 observed in 2002
sp/* . 10 FITS tables with spectra
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Cluster Globular cluster name
9- 13 A5 --- Star Star name
15- 16 I2 h RAh Right Ascension (J2000)
18- 19 I2 min RAm Right Ascension (J2000)
21- 26 F6.3 s RAs Right Ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 39 F5.2 arcsec DEs Declination (J2000)
41- 52 A12 --- RunId Identification of observing run
54- 62 A9 --- 69D0231B Name of the column with fluxes in the FITS
tables NGC638869D0231BBLUE_flux.fits
(329.43430nm-451.8527nm),
NGC638869D0231BREDL_flux.fits
(461.84839nm-558.80300nm) and
NGC638869D0231BREDU_flux.fits
(568.81700nm-661.27090nm)
64- 72 A9 --- 69D0220B Name of the column with fluxes in the FITS
tables NGC639769D0220BBLUE_flux.fits
(329.49800nm-452.06592nm),
NGC639769D0220BREDL_flux.fits
(461.99531-559.01172nm) and
NGC639769D0220BREDU_flux.fits
(568.99438nm-665.00591nm)
74- 83 A10 --- 65L0233A Name of the column with fluxes in the FITS
table NGC675265L0233ABLUE_flux.fits
(377.05330nm-498.08198nm)
85- 94 A10 --- 69D0220A Name of the column with fluxes in the FITS
tables NGC675269D0220ABLUE_flux.fits
(329.51750nm-452.05420nm),
NGC675269D0220AREDL_flux.fits
(462.02388nm-559.06499nm) and
NGC675269D0220AREDU_flux.fits
(569.02949nm-663.07930nm)
96-126 A31 --- FileBLUE Name of the fits file BLUE in subdirectory sp
128-158 A31 --- FileREDL Name of the fits file REDL in subdirectory sp
160-190 A31 --- FileREDU Name of the fits file REDU in subdirectory sp
192-193 I2 --- Rank Column number in the fits file for the
corresponding flux
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Byte-by-byte Description of file: ngc*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star name
7- 15 F9.4 0.1nm lambda Wavelength in Å
19- 24 F6.2 0.1pm EWlambda Equivalent width in mÅ
29- 34 F6.3 0.1pm e_EWlambda Error of equivalent width in mÅ
38- 42 A5 --- IonCode Code of the ion
(atomicnumber.ionizationlevel)
46- 50 F5.2 [-] loggf logarithm of the oscillator strength
53- 58 F6.3 eV chi Excitation potential
64- 67 F4.2 [-] loggamRad logarithm of the radiative damping constant
70- 74 F5.2 [-] loggamStark logarithm of the Stark damping constant
77- 81 F5.2 [-] loggamVdW logarithm of the Van der Waals damping
constant
85- 88 F4.2 --- VelParam [0] velocity parameter alpha (always 0)
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Acknowledgements:
Sabine Moehler, smoehler(at)eso.org
(End) Patricia Vannier [CDS] 09-Dec-2024