The discovery of Mg II λ4481 in the white dwarf EG 102: Evidence for ongoing accretion

J. B. Holberg; M. A. Barstow; Elizabeth M. Green

doi:10.1086/310446

The discovery of Mg II λ4481 in the white dwarf EG 102: Evidence for ongoing accretion

J. B. Holberg, M. A. Barstow, Elizabeth M. Green

Steward Observatory

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40 Scopus citations

Abstract

Recent optical spectra of the DA3 white dwarf EG 102 clearly show a feature due to Mg II λ4481. This is the first spectroscopic detection of Mg in a DA star at a temperature of 20,000 K. The presence of this ion in the stellar photosphere poses a severe dilemma for the theory of radiative levitation, which predicts a vanishingly small equilibrium abundance of Mg in a star such as EG 102. Ongoing accretion must to be the source of this ion. An accretion rate of 1.6 × 10^-16 M_⊙ yr^-1 is implied by the short timescale (3.3 days) for the diffusive loss of Mg from the photosphere. Such a rate could be supplied by the interstellar medium, if EG 102 is embedded in a diffuse interstellar cloud. Alternately, EG 102 may possess a very low mass companion, which is transferring material onto the white dwarf. Finally, we use an IUE echelle spectrum to demonstrate the presence of photospheric Si in this star. We find respective abundances of log (Mg/H) = -5.3 and log (Si/H) = -7.0 for EG 102.

Original language	English (US)
Pages (from-to)	L127-L130
Journal	Astrophysical Journal
Volume	474
Issue number	2 PART II
DOIs	https://doi.org/10.1086/310446
State	Published - 1997

Keywords

Stars: abundances
Stars: individual (EG 102)
Stars: white dwarfs

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1086/310446

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@article{47542174fd23432393ac3b82a708105a,

title = "The discovery of Mg II λ4481 in the white dwarf EG 102: Evidence for ongoing accretion",

abstract = "Recent optical spectra of the DA3 white dwarf EG 102 clearly show a feature due to Mg II λ4481. This is the first spectroscopic detection of Mg in a DA star at a temperature of 20,000 K. The presence of this ion in the stellar photosphere poses a severe dilemma for the theory of radiative levitation, which predicts a vanishingly small equilibrium abundance of Mg in a star such as EG 102. Ongoing accretion must to be the source of this ion. An accretion rate of 1.6 × 10-16 M⊙ yr-1 is implied by the short timescale (3.3 days) for the diffusive loss of Mg from the photosphere. Such a rate could be supplied by the interstellar medium, if EG 102 is embedded in a diffuse interstellar cloud. Alternately, EG 102 may possess a very low mass companion, which is transferring material onto the white dwarf. Finally, we use an IUE echelle spectrum to demonstrate the presence of photospheric Si in this star. We find respective abundances of log (Mg/H) = -5.3 and log (Si/H) = -7.0 for EG 102.",

keywords = "Stars: abundances, Stars: individual (EG 102), Stars: white dwarfs",

author = "Holberg, {J. B.} and Barstow, {M. A.} and Green, {Elizabeth M.}",

note = "Funding Information: We wish to thank Ivan Hubeny and Thierry Lanz for their assistance with the TLUSTY program, Jim Collins for his help with the IUE data, and Ed Sion for useful discussions. We also wish to acknowledge use of the diffusion time scale for Mg calculated by Jean Dupuis. IUE Data Analysis Center (IUEDAC) and the National Space Science Data Center (NSSDC) are acknowledged for providing the archive spectra presented here. J. B. H. wishes to acknowledge support by NASA grants NAG5-434 and NAGW5-2269. M. A. B. wishes to acknowledge the support of PPARC, UK, and the Royal Society through provision of research grants.",

year = "1997",

doi = "10.1086/310446",

language = "English (US)",

volume = "474",

pages = "L127--L130",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "IOP Publishing Ltd.",

number = "2 PART II",

}

TY - JOUR

T1 - The discovery of Mg II λ4481 in the white dwarf EG 102

T2 - Evidence for ongoing accretion

AU - Holberg, J. B.

AU - Barstow, M. A.

AU - Green, Elizabeth M.

N1 - Funding Information: We wish to thank Ivan Hubeny and Thierry Lanz for their assistance with the TLUSTY program, Jim Collins for his help with the IUE data, and Ed Sion for useful discussions. We also wish to acknowledge use of the diffusion time scale for Mg calculated by Jean Dupuis. IUE Data Analysis Center (IUEDAC) and the National Space Science Data Center (NSSDC) are acknowledged for providing the archive spectra presented here. J. B. H. wishes to acknowledge support by NASA grants NAG5-434 and NAGW5-2269. M. A. B. wishes to acknowledge the support of PPARC, UK, and the Royal Society through provision of research grants.

PY - 1997

Y1 - 1997

N2 - Recent optical spectra of the DA3 white dwarf EG 102 clearly show a feature due to Mg II λ4481. This is the first spectroscopic detection of Mg in a DA star at a temperature of 20,000 K. The presence of this ion in the stellar photosphere poses a severe dilemma for the theory of radiative levitation, which predicts a vanishingly small equilibrium abundance of Mg in a star such as EG 102. Ongoing accretion must to be the source of this ion. An accretion rate of 1.6 × 10-16 M⊙ yr-1 is implied by the short timescale (3.3 days) for the diffusive loss of Mg from the photosphere. Such a rate could be supplied by the interstellar medium, if EG 102 is embedded in a diffuse interstellar cloud. Alternately, EG 102 may possess a very low mass companion, which is transferring material onto the white dwarf. Finally, we use an IUE echelle spectrum to demonstrate the presence of photospheric Si in this star. We find respective abundances of log (Mg/H) = -5.3 and log (Si/H) = -7.0 for EG 102.

AB - Recent optical spectra of the DA3 white dwarf EG 102 clearly show a feature due to Mg II λ4481. This is the first spectroscopic detection of Mg in a DA star at a temperature of 20,000 K. The presence of this ion in the stellar photosphere poses a severe dilemma for the theory of radiative levitation, which predicts a vanishingly small equilibrium abundance of Mg in a star such as EG 102. Ongoing accretion must to be the source of this ion. An accretion rate of 1.6 × 10-16 M⊙ yr-1 is implied by the short timescale (3.3 days) for the diffusive loss of Mg from the photosphere. Such a rate could be supplied by the interstellar medium, if EG 102 is embedded in a diffuse interstellar cloud. Alternately, EG 102 may possess a very low mass companion, which is transferring material onto the white dwarf. Finally, we use an IUE echelle spectrum to demonstrate the presence of photospheric Si in this star. We find respective abundances of log (Mg/H) = -5.3 and log (Si/H) = -7.0 for EG 102.

KW - Stars: abundances

KW - Stars: individual (EG 102)

KW - Stars: white dwarfs

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JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2 PART II

ER -

The discovery of Mg II λ4481 in the white dwarf EG 102: Evidence for ongoing accretion

Abstract

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