First results from the Goddard High-Resolution Spectrograph: Evidence for photospheric microturbulence in early O stars: Are surface gravities systematically underestimated?

Ivan - Hubeny, S. R. Heap, B. Altner

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

GHRS spectra of two very hot stars (BD +75°325 and Melnick 42) provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, we have built theoretical models in which the microturbulence is allowed to modify not only the Doppler line widths (classical "spectroscopic" microturbulence), but also the turbulent pressure (thus mimicking a "physical" turbulence). We find that a corresponding modification of the temperature-pressure stratification influences the hydrogen and helium line profiles to the extent that the surface gravities of early O stars determined without considering microturbulence are too low by 0.1-0.15 dex. Thus, including microturbulence would reduce, or resolve completely, a long-standing discrepancy between evolutionary and spectroscopic stellar masses.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume377
Issue number1 PART II
StatePublished - 1991
Externally publishedYes

Fingerprint

early stars
O stars
spectrographs
gravity
gravitation
hot stars
high resolution
photosphere
stratification
stellar mass
helium
turbulence
hydrogen
profiles
temperature

Keywords

  • Stars: early-type
  • Stars: massive
  • Stars: subdwarfs
  • Stars: winds
  • Turbulence
  • Ultraviolet: spectra

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

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title = "First results from the Goddard High-Resolution Spectrograph: Evidence for photospheric microturbulence in early O stars: Are surface gravities systematically underestimated?",
abstract = "GHRS spectra of two very hot stars (BD +75°325 and Melnick 42) provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, we have built theoretical models in which the microturbulence is allowed to modify not only the Doppler line widths (classical {"}spectroscopic{"} microturbulence), but also the turbulent pressure (thus mimicking a {"}physical{"} turbulence). We find that a corresponding modification of the temperature-pressure stratification influences the hydrogen and helium line profiles to the extent that the surface gravities of early O stars determined without considering microturbulence are too low by 0.1-0.15 dex. Thus, including microturbulence would reduce, or resolve completely, a long-standing discrepancy between evolutionary and spectroscopic stellar masses.",
keywords = "Stars: early-type, Stars: massive, Stars: subdwarfs, Stars: winds, Turbulence, Ultraviolet: spectra",
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year = "1991",
language = "English (US)",
volume = "377",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 PART II",

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TY - JOUR

T1 - First results from the Goddard High-Resolution Spectrograph

T2 - Evidence for photospheric microturbulence in early O stars: Are surface gravities systematically underestimated?

AU - Hubeny, Ivan -

AU - Heap, S. R.

AU - Altner, B.

PY - 1991

Y1 - 1991

N2 - GHRS spectra of two very hot stars (BD +75°325 and Melnick 42) provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, we have built theoretical models in which the microturbulence is allowed to modify not only the Doppler line widths (classical "spectroscopic" microturbulence), but also the turbulent pressure (thus mimicking a "physical" turbulence). We find that a corresponding modification of the temperature-pressure stratification influences the hydrogen and helium line profiles to the extent that the surface gravities of early O stars determined without considering microturbulence are too low by 0.1-0.15 dex. Thus, including microturbulence would reduce, or resolve completely, a long-standing discrepancy between evolutionary and spectroscopic stellar masses.

AB - GHRS spectra of two very hot stars (BD +75°325 and Melnick 42) provide evidence for the presence of microturbulence in their photospheres. In attempting to reproduce the observed spectra, we have built theoretical models in which the microturbulence is allowed to modify not only the Doppler line widths (classical "spectroscopic" microturbulence), but also the turbulent pressure (thus mimicking a "physical" turbulence). We find that a corresponding modification of the temperature-pressure stratification influences the hydrogen and helium line profiles to the extent that the surface gravities of early O stars determined without considering microturbulence are too low by 0.1-0.15 dex. Thus, including microturbulence would reduce, or resolve completely, a long-standing discrepancy between evolutionary and spectroscopic stellar masses.

KW - Stars: early-type

KW - Stars: massive

KW - Stars: subdwarfs

KW - Stars: winds

KW - Turbulence

KW - Ultraviolet: spectra

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