The spectroscopic binary system Gl 375

Díaz, R. F.; González, J. F.; Cincunegui, C.; Mauas, P. J. D.

doi:10.1051/0004-6361:20078195

Cited by 26 publications

(39 citation statements)

References 23 publications

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“…We divided the flux in the central line by the flux in two reference lines of 10.75 and 8.75 Å centered at 6550.87 and 6580.31 Å, respectively. Díaz et al (2007b) proposed that the Na i D1 and D2 lines could also be used to follow the chromospheric activity level of very active late-type stars with (B − V) > 1.1. In this sample we do not have very active stars, but we decided to study these lines as a complement to the other widely used activity proxies.…”

Section: Activity Indicesmentioning

confidence: 99%

“…The Na i D lines provide information about the conditions in the middle-to-lower chromosphere (Mauas 2000) and thus are a good complement to the upper chromosphere indicator Hα and lower chromosphere proxy Ca ii index. We first computed our Na i index in a similar fashion as Díaz et al (2007b) by calculating the average flux in the core of the D1 (λ5895.92) and D2 (λ5889.95) lines using 1 Å bands. We used two reference bands with windows of 10 and 20 Å centered at 5805.0 and 6090.0 Å, respectively.…”

Section: Activity Indicesmentioning

confidence: 99%

“…More recently, evidence for cyclic activity was found for a few M dwarfs. Cincunegui et al (2007a) claimed a magnetic cycle with a ∼442 day period for the dMe 5.5 Prox Centauri & Díaz et al (2007b) found a P =∼ 763 day activity period for the dMe 3.5 spectroscopic binary Gl375. Aditionally, activity cycles were also claimed to be present on Gl229A (M1/2) and Gl752A (M2.5) with periods of A&A 534, A30 (2011) ∼4 yr and ∼7 yr, respectively (Buccino et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program

Silva

Santos

Bonfils

et al. 2011

A&A

185

164

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Context. The search for extra-solar planets similar to Earth is becoming a reality, but as the level of the measured radial-velocity reaches the sub-m s −1 , stellar intrinsic sources of noise capable of hiding the signal of these planets from scrutiny become more important. Aims. Other stars are known to have magnetic cycles similar to that of the Sun. The relationship between these activity variations and the observed radial-velocity is still not satisfactorily understood. Following our previous work, which studied the correlation between activity cycles and long-term velocity variations for K dwarfs, we now expand it to the lower end of the main sequence. In this first paper our aim is to assess the long-term activity variations in the low end of the main sequence, having in mind a planetary search perspective. Methods. We used a sample of 30 M0-M5.5 stars from the HARPS M-dwarf planet search program with a median timespan of observations of 5.2 years. We computed chromospheric activity indicators based on the Ca ii H and K, Hα, He i D3, and Na i D1 and D2 lines. All data were binned to average out undesired effects such as rotationally modulated atmospheric inhomogeneities. We searched for long-term variability of each index and determined the correlations between them. Results. While the S Ca II , Hα, and Na i indices showed significant variability for a fraction of our stellar sample (39%, 33%, and 37%, respectively), only 10% of our stars presented significant variability in the He i index. We therefore conclude that this index is a poor activity indicator at least for this type of stars. Although the Hα shows good correlation with S Ca II for the most active stars, the correlation is lost when the activity level decreases. This result appears to indicate that the Ca ii−Hα correlation is dependent on the activity level of the star. The Na i lines correlate very well with the S Ca II index for the stars with low activity levels we used, and are thus a good chromospheric activity proxy for early-M dwarfs. We therefore strongly recommend the use of the Na i activity index because the signal-to-noise ratio in the sodium lines spectral region is always higher than for the calcium lines.

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Section: Activity Indicesmentioning

confidence: 99%

Section: Activity Indicesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program

Silva

Santos

Bonfils

et al. 2011

A&A

185

164

View full text Add to dashboard Cite

show abstract

“…Vida et al (2013) studied four systems (one K3, one M4, and the others ∼M1) with very short rotation periods (∼0.45 days) and found similarly short cycles ranging from 0.84 to 1.45 yr in all except the M4. Other nearly-fully convective stars showing signs of a cycle include AD Leo (M3; Buccino et al 2014), GJ375 (M3; Díaz et al 2007), and perhaps EV Lac (M3.5; Alekseev 2005).…”

Section: Introductionmentioning

confidence: 99%

“…Benedict et al (1998), analyzing 5 years of photometry data from the Hubble Fine Guidance Sensors, suggested a 3.0-year cycle, though with low confidence. Cincunegui et al (2007), measuring the Hα line-to-continuum on 24 nights over 7 years and excluding obvious flares, made Lomb-Scargle periodograms and found a 1.2-year period with peak-to-peak amplitude variations of 25% but a False Alarm Probability of 35%. Lastly, Endl & Kürster (2008) found an 'intriguing peak' in 76 nights of radial velocity measurements, but the period of that peak roughly matches the seven year span (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) of their observing program, and they did not see evidence for an 83-d rotation period (see below).…”

Section: Introductionmentioning

confidence: 99%

Optical, UV, and X-ray evidence for a 7-yr stellar cycle in Proxima Centauri

Wargelin¹,

Saar²,

Pojmański³

et al. 2016

Mon. Not. R. Astron. Soc.

103

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Stars of stellar type later than about M3.5 are believed to be fully convective and therefore unable to support magnetic dynamos like the one that produces the 11-year solar cycle. Because of their intrinsic faintness, very few late M stars have undergone long-term monitoring to test this prediction, which is critical to our understanding of magnetic field generation in such stars. Magnetic activity is also of interest as the driver of UV and X ray radiation, as well as energetic particles and stellar winds, that affect the atmospheres of close-in planets that lie within habitable zones, such as the recently discovered Proxima b. We report here on several years of optical, UV, and X-ray observations of Proxima Centauri (GJ 551; dM5.5e): 15 years of ASAS photometry in the V band (1085 nights) and 3 years in the I band (196 nights), 4 years of Swift XRT and UVOT observations (more than 120 exposures), and 9 sets of X-ray observations from other X-ray missions (ASCA, XMM-Newton, and three Chandra instruments) spanning 22 years. We confirm previous reports of an 83-day rotational period and find strong evidence for a 7-year stellar cycle, along with indications of differential rotation at about the solar level. X-ray/UV intensity is anti-correlated with optical V -band brightness for both rotational and cyclical variations. From comparison with other stars observed to have X-ray cycles we deduce a simple empirical relationship between X-ray cyclic modulation and Rossby number, and we also present Swift UV grism spectra covering 2300-6000Å.

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12 years of stellar activity observations in Argentina

Mauas¹,

Buccino²,

Díaz³

et al. 2011

Proc. IAU

Self Cite

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Abstract. We present an observational program we started in 1999, to systematically obtain mid-resolution spectra of late-type stars, to study in particular chromospheric activity. In particular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigated the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar color, and it is not always preserved when simultaneous observations of a particular star are considered. We also used our observations to model the chromospheres of stars of different spectral types and activity levels, and found that the integrated chromospheric radiative losses, normalized to the surface luminosity, show a unique trend for G and K dwarfs when plotted against the S index.

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The spectroscopic binary system Gl 375

Cited by 26 publications

References 23 publications

Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program

Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program

Optical, UV, and X-ray evidence for a 7-yr stellar cycle in Proxima Centauri

12 years of stellar activity observations in Argentina

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