J/A+A/638/A157 Massive O-type stars near ZAMS elusive detection (Holgado+, 2020)
The IACOB project.
VI. On the elusive detection of massive O-type stars close to the ZAMS.
Holgado G., Simon-Diaz S., Haemmerle L., Lennon D.J., Barba R.H.,
Cervino M., Castro N., Herrero A., Meynet G., Arias J.I.
<Astron. Astrophys. 638, A157 (2020)>
=2020A&A...638A.157H 2020A&A...638A.157H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, early-type ; Stars, O ; Effective temperatures ;
Extinction ; Spectroscopy
Keywords: stars: early-type - stars: massive -
Hertzsprung-Russell and C-M diagrams - stars: evolution -
stars: formation - techniques: spectroscopic
Abstract:
The apparent lack of massive O-type stars near the Zero Age Main
Sequence, or ZAMS, (at ages <2Myr) has been a topic widely discussed
in the last 40 years. Different explanations for the elusive detection
of these young massive stars have been proposed from both the
observational and theoretical side, but no firm conclusions have been
reached yet.
The aim of this work is to perform a reassessment of this empirical
result benefiting from the high quality spectroscopic observations of
(more than 400) Galactic O-type stars gathered by the IACOB and OWN
surveys.
We use effective temperatures and surface gravities resulting from a
homogeneous, semi-automatized, IACOB-GBAT/FASTWIND spectroscopic
analysis to locate our sample of stars in the Kiel and spectroscopic
Hertzsprung-Russell (HR) diagrams. We evaluate the completeness of our
magnitude limited sample of stars - as well as the existence of
potential observational biases affecting the compiled sample - using
information from the Galactic O star catalog (GOSC). We discuss
limitations and possible systematics of our analysis methodology, and
compare our results with other recent studies using smaller samples of
Galactic O-type stars. We mainly base our discussion on the
distribution of stars in the spectroscopic HR diagram in order to
avoid the use of still uncertain distances to most of the stars in our
sample. However, we also perform a more detailed study of the young
cluster Trumpler-14 as an illustrative example of how Gaia cluster
distances can help to construct the associated classical HR diagram.
We find that the apparent lack of massive O-type stars near the
zero-age main sequence with initial evolutionary masses in the range
between ∼30 and 70M☉ still persist despite using spectroscopic
results from a large, non-biased sample of stars. We do not find any
correlations between the dearth of stars close to the ZAMS and obvious
observational biases, limitations of our analysis methodology, and/or
the use of one example spectroscopic HR diagram instead of the
classical one. Finally, by investigating the impact of the efficiency
of mass accretion during the formation process of massive stars, we
conclude that an adjustment of the mass accretion rate towards lower
values than canonically assumed could reconcile the hotter boundary of
the empirical distribution of optically detected O-type stars in the
spectroscopic HR diagram and the theoretical birthline for stars with
masses above 30M☉. Last, we also discuss how the presence of a
small sample of O2-O3.5 stars found much closer to the ZAMS than the
main distribution of Galactic O-type star could be explained in the
context of this scenario taking also into account the effect of
non-standard star evolution (e.g. binary interaction, mergers, and/or
homogeneous evolution).
Description:
List of the 285 stars with spectroscopic parameters obtained in this
work. We performed an exhaustive search for spectra of these stars in
modern high resolution spectroscopic databases. The spectrum with best
quality, in terms of signal-to-noise ratio, was considered for the
quantitative spectroscopic analysis and a multi-epoch
characterization.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablee1.dat 98 285 O-type stars considered in this work with
spectroscopic parameters
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See also:
J/A+A/562/A135 : Northern Galactic OB stars vsini (Simon-Diaz+, 2014)
J/A+A/597/A22 : Massive O- and B-type stars velocities (Simon-Diaz+, 2017)
J/A+A/613/A65 : Spectroscopic parameters of O-type stars (Holgado+, 2018)
J/A+A/613/A9 : Extinction towards Galactic O stars (Maiz Apellaniz+, 2018)
Byte-by-byte Description of file: tablee1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Target Star name
17- 21 A5 --- SpType Spectral type
23- 35 A13 --- LumClass Luminosity class
37 A1 --- l_Teff Limit flag on Teff
38- 41 F4.1 kK Teff Effective temperature
43- 45 F3.1 kK e_Teff ? Effective temperature error
47 A1 --- l_loggt Limit flag on loggt
48- 51 F4.2 [cm/s2] loggt Gravity corrected from rotational effects
53- 56 F4.2 [cm/s2] e_loggt ? Gravity corrected from rotational
effects error
58 A1 --- l_logLsp Limit flag on logLsp-Lspo
59- 62 F4.2 [Lsun] logLsp Lsp parameter (1)
64- 67 F4.2 [Lsun] e_logLsp ? Lsp parameter error
69- 72 F4.1 mag Bmag B magnitude
74- 78 F5.3 mag E(4405-5495) ? E(4405-5495) extinction
80- 98 A19 --- Notes Multi-epoch notes
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Note (1): Lsp=Teff4/gt, gt=g+gc, gc=(Vrot*sini)2/R*.
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Acknowledgements:
Gonzalo Holgado, gholgado(at)cab.inta-csic.es
References:
Simon-Diaz & Herrero, Paper I 2014A&A...562A.135S 2014A&A...562A.135S, Cat. J/A+A/562/A135
Simon-Diaz et al., Paper II 2014A&A...570L...6S 2014A&A...570L...6S
Simon-Diaz et al., Paper III 2017A&A...597A..22S 2017A&A...597A..22S, Cat, J/A+A/597/A22
Godart et al., Paper IV 2017A&A...597A..23G 2017A&A...597A..23G
Holgado et al., Paper V 2018A&A...613A..65H 2018A&A...613A..65H, Cat. J/A+A/613/A65
Maiz-Apellaniz & Barba, 2018A&A...613A...9M 2018A&A...613A...9M, Cat. J/A+A/613/A9
(End) Gonzalo Holgado [CAB (INTA-CSIC)], Patricia Vannier [CDS] 18-May-2020