M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale

Gizis, John E.

doi:10.1086/118302

Cited by 330 publications

(646 citation statements)

References 40 publications

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“…Band indices measuring the TiO and CaH feature have been the basis of modern M subdwarf classification systems (Gizis 1997;Lépine et al 2007) and have been used by many different groups, though Jao et al (2008) ζ parameter uses these indices to construct a metallicity indicator independent of temperature (Lépine et al 2007). The carbon-rich models shown in Figure 2 predicted a numerically larger TiO5 index at a given CaH2 (or T eff , which is less easily measured).…”

Section: Observational Constraintsmentioning

confidence: 99%

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M dwarfs and the fraction of high carbon-to-oxygen stars in the solar neighbourhood

Gizis

Marks

Hauschildt³

2015

Mon. Not. R. Astron. Soc.

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We investigate the frequency of high carbon-to-oxygen (C/O = 0.9) M dwarf stars in the solar neighbourhood. Using synthetic spectra, we find that such M dwarfs would have weaker TiO bands relative to hydride features. Similar weakening has already been detected in M-subdwarf (sdM) stars. By comparing to existing spectroscopic surveys of nearby stars, we show that less than one percent of nearby stars have high carbon-to-oxygen ratios. This limit does not include stars with C/O= 0.9, [m/H]> 0.3, and [C/Fe]> 0.1, which we predict to have low-resolution optical spectra similar to solar metallicity M dwarfs.

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Section: Observational Constraintsmentioning

confidence: 99%

“…The brightest sdM star in that sample is GJ 781. GJ 781 has a high space velocity and lies in the subdwarf region of the H-R diagram (Gizis 1997); it has an unseen white dwarf companion (Gizis 1998) and a metal-poor T8 brown dwarf companion (Mace et al 2013). Another small ζ parameter star is LSPM J2319+7900S.…”

Section: Observational Constraintsmentioning

confidence: 99%

M dwarfs and the fraction of high carbon-to-oxygen stars in the solar neighbourhood

Gizis

Marks

Hauschildt³

2015

Mon. Not. R. Astron. Soc.

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“…Kirkpatrick et al 1991;Gizis 1997;Lépine et al 2013) so we relied instead on the overall shape of the spectrum.…”

Section: Spectral Typingmentioning

confidence: 99%

Spectrophotometric characterization of high proper motion sources fromWISE

Beamín

Ivanov

Minniti

et al. 2015

Mon. Not. R. Astron. Soc.

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The census of the solar neighborhood is almost complete for stars and becoming more complete in the brown dwarf regime. Spectroscopic, photometric and kinematic characterization of nearby objects helps us to understand the local mass function, the binary fraction, and provides new targets for sensitive planet searches. We aim to derive spectral types and spectro-photometric distances of a sample of new high proper motion sources found with the WISE satellite, and obtain parallaxes for those objects that fall within the area observed by the Vista Variables in the Vía Láctea survey (VVV). We used low resolution spectroscopy and template fitting to derive spectral types, multiwavelength photometry to characterize the companion candidates and obtain photometric distances. Multi-epoch imaging from the VVV survey was used to measure the parallaxes and proper motions for three sources. We confirm a new T2 brown dwarf within ∼15 pc. We derived optical spectral types for twenty four sources, mostly M dwarfs within 50 pc. We addressed the wide binary nature of sixteen objects found by the WISE mission and previously known high proper motion sources. Six of these are probably members of wide binaries, two of those are new, and present evidence against the physical binary nature of two candidate binary stars found in the literature, and eight that we selected as possible binary systems. We discuss a likely microlensing event produced by a nearby low mass star and a galaxy, that is to occur in the following five years.

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“…Our results were sensitive to the assumed limb-darkening coefficient, ò, with an ∼15 km s −1 deviation in v sin i for a change Δò∼0.1. Due to this sensitivity, we used the Claret (2000) linear limb-darkening coefficient catalog for each source, using characteristic values of g log and effective temperatures (Gizis 1997;Casagrande et al 2008;Rajpurohit et al 2013) for their literature SpTs (for G and K stars) and those determined by their TiO-7140 indices (for M stars; see Section 3.3).…”

Section: Rotational Velocitiesmentioning

confidence: 99%

Searching for Spectroscopic Binaries Within Transition Disk Objects*

Kohn

Shkolnik

Weinberger

et al. 2016

ApJ

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Transition disks (TDs) are intermediate stage circumstellar disks characterized by an inner gap within the disk structure. To test whether these gaps may have been formed by closely orbiting, previously undetected stellar companions, we collected high-resolution optical spectra of 31 TD objects to search for spectroscopic binaries (SBs). Twenty-four of these objects are in Ophiuchus and seven are within the Coronet, Corona Australis, and Chameleon I star-forming regions. We measured radial velocities for multiple epochs, obtaining a median precision of 400 ms −1 . We identified double-lined SB SSTc2d J163154.7-250324 in Ophiuchus, which we determined to be composed of a K7(±0.5) and a K9(±0.5) star, with orbital limits of a<0.6 au and P<150 days. This results in an SB fraction of -+ 0.04 0.03 0.12 in Ophiuchus, which is consistent with other spectroscopic surveys of non-TD objects in the region. This similarity suggests that TDs are not preferentially sculpted by the presence of close binaries and that planet formation around close binaries may take place over similar timescales to that around single stars.

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M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale

Cited by 330 publications

References 40 publications

M dwarfs and the fraction of high carbon-to-oxygen stars in the solar neighbourhood

M dwarfs and the fraction of high carbon-to-oxygen stars in the solar neighbourhood

Spectrophotometric characterization of high proper motion sources fromWISE

Searching for Spectroscopic Binaries Within Transition Disk Objects*

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