Measurements of Starspot Area and Temperature on Five Active, Evolved Stars

O'Neal, Douglas; Saar, Steven H.; Neff, J. E.

doi:10.1086/177288

Cited by 95 publications

(92 citation statements)

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“…Molecular lines have been or can profitably be used to probe cool gas, e.g., in the chromosphere (e.g., Ayres & Testerman 1981;Ayres et al 1986;Uitenbroek et al 1994), in the umbrae of sunspots (e.g., Sotirovski 1972;Boyer 1978;Wöhl 1971) or on stars and in starspots (e.g., Ramsey & Nations 1980;Neff et al 1995;O'Neal et al 1996). Due to their high temperature sensitivity molecular lines provide enhanced contrast in images.…”

Section: Discussionmentioning

confidence: 99%

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The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

Berdyugina

Solanki

Frutiger

2003

A&A

122

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Abstract. Recent advances in the computation of the Zeeman splitting of molecular lines have paved the way for their use as diagnostics of solar and stellar magnetic fields. A systematic study of their diagnostic capabilities had not been carried out so far, however. Here we investigate how molecular lines can be used to deduce the magnetic and thermal structure of sunspots, starspots and cool stars. First, we briefly describe the Stokes radiative transfer of Zeeman-split molecular lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and investigate their diagnostic capabilities. We also compare the synthetic profiles with observations. Spectra of TiO, OH and FeH are found to be interesting diagnostics of sunspot magnetic fields. This is also true for cool stars, where, however, the OH Stokes V profiles may require very high S/N data to be reliably employed. Finally we investigate the potential of various molecular bands for high-contrast imaging of the solar surface. The violet CN and CH bands turn out to be most promising for imaging the photosphere, the TiO bands are excellent for imaging sunspot umbrae, while the UV OH band can be used for imaging both the photosphere and sunspots.

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Section: Discussionmentioning

confidence: 99%

“…Further observations revealed TiO bands in the spectra of other active stars of sufficiently early spectral type, which allowed the spot area and temperature to be measured (e.g. Neff et al 1995;O'Neal et al 1996).…”

Section: Tiomentioning

confidence: 99%

The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

Berdyugina

Solanki

Frutiger

2003

A&A

122

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“…This resulted in a maximum V magnitude of 6.59. O'Neal et al (1996) showed that on some heavily spotted stars the observed maximum V magnitude underestimates the brightness of the unspotted star by 0.3-0.4 mag. Nevertheless, we have adopted the historical maximum as the unspotted V magnitude of the primary since for HD 37824 we are unable to determine a specific correction.…”

Section: Basic Propertiesmentioning

confidence: 97%

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Fekel

Henry

2005

Astron J

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We have obtained spectroscopy and photometry of three chromospherically active, single-lined spectroscopic binaries, HD 37824 (V1149 Ori), HD 181809 (V4138 Sgr), and HD 217188 (AZ Psc). HD 37824 has a circular orbit with a period of 53.57 days. Its primary is a K0 III star, while the secondary is likely a G or K dwarf. HD 181809 has an orbit with a period of 13.04667 days and a low eccentricity of 0.040. The primary has a spectral type of K0 III-IV, and its secondary is probably an M dwarf. The orbit of HD 217188 has a period of 47.1209 days and a moderately high eccentricity of 0.470. The spectral type of the primary is K0 III, while the secondary is likely an M dwarf. All three systems are estimated to have near solar iron abundances. Photometric observations spanning 15-16 years for all three stars yield mean photometric periods of 53.12, 59.85, and 90.89 days for HD 37824, HD 181809, and HD 217188, respectively. Thus, HD 37824 is rotating synchronously with the orbital period, while HD 181809 and HD 217188 are both rotating considerably slower than synchronously. All three stars show longterm variations in mean brightness and photometric amplitude, but no correlations are observed between the seasonal mean brightness, photometric amplitude, and seasonal photometric period in any of the stars. No clear evidence for long-term periodic variations in any of these parameters is present. The circular orbit of HD 37824 and the synchronous rotation of its K giant argue that the star is in the core helium-burning phase of its evolution. The giant components of HD 181809 and HD 217188 are asynchronous rotators, and both systems have eccentric orbits. Thus, those two stars are likely first-ascent giants.

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“…TiO bands are observed in the spectra of cool stars (spectral types later than $K5). The molecular bands (as well as other molecular lines) are also seen in the isolated spectra of sunspots, where the umbral temperatures are typically about 4200 K. In addition, spectroscopy of several RS CVn stars reveals the presence of TiO molecular bands in stars with photospheric temperatures normally too hot to have TiO molecules, indicating that TiO features originate in cool starspot regions (Ramsey & Nations 1980;Neff et al 1995;O'Neal et al 1996). Thus, TiO band photometry using narrowband filters is very useful in identifying and defining starspots on chromospherically active stars where cool starspots are believed to cover large fractions of the stellar photospheres.…”

Section: Introductionmentioning

confidence: 92%

“…The modeling is insensitive to any contribution of spots that are evenly distributed around the star similar to sunspot distributions. Neff, O'Neal, & Saar (1995), O'Neal & Neff (1997), O'Neal, Saar, & Neff (1996), O'Neal, Saar (1998), andO'Neal et al (2001) have used another method to investigate starspots on RS Canum Venaticorum stars using titanium oxide (TiO) molecular features as absolute indicators of cool regions where TiO can be present. TiO bands are observed in the spectra of cool stars (spectral types later than $K5).…”

Section: Introductionmentioning

confidence: 99%

Wing Near-Infrared, TiO-Band, andV-Band Photometry of Chromospherically Active Star Andromedae

2003

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As a pilot program, Wing near-IR, TiO-band, and V-band photometry is being conducted of the RS Canum Venaticorum type, chromospherically active, G8 IV-III star Andromedae. The objective is to investigate a possible relationship between variation of the $54 day rotationally starspot modulated visual light curve and TiO absorption strength. The TiO ( , 0, 0) absorption band strength at = 719 nm is very sensitive to temperature for cool stars and manifests itself in cooler starspot regions (T 4000 K). TiO photometry has an advantage over conventional photometry in that it provides unambiguous measures of the fractional cool starspot coverage. In addition, as the stars rotate, the variation in the TiO index yields information about the longitudinal distribution of the starspots. Importantly, combining the TiO photometry with the V-band and near-IR light curves allows the discrimination of white-light faculae (=hot spot) and cool starspot contributions. Initial results of this study indicate that the observed V-band and near-IR continua light variations found for And primarily arise from bright spot (plage) features rather than dark starspots as is usually assumed. This is in contrast to current theories that the visual light variation is solely due to dark spots. Models using both bright and dark spot features have been developed and are being used to fit the light and TiO-index curves. The models account for cool/hot spot characteristics such as projected filling factor and temperature. The long-term variation of V light and TiO index have been investigated to search for any activity cycles.

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Measurements of Starspot Area and Temperature on Five Active, Evolved Stars

Cited by 95 publications

References 0 publications

The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

The molecular Zeeman effect and diagnostics of solar and stellar magnetic fields

Chromospherically Active Stars. XXIV. The Giant, Single-lined Binaries HD 37824, HD 181809, and HD 217188

Wing Near-Infrared, TiO-Band, andV-Band Photometry of Chromospherically Active Star Andromedae

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