TIGRE: A new robotic spectroscopy telescope at Guanajuato, Mexico

Schröder

Rauw

et al. 2016

A&A

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We present a new radial velocity curve for the two components of the eclipsing spectroscopic binary α CrB. This binary consists of two main-sequence stars of types A and G in a 17.3599-day orbit, according to the data from our robotic TIGRE facility that is located in Guanajuato, Mexico. We used a high-resolution solar spectrum to determine the radial velocities of the weak secondary component by cross-correlation and wavelength referencing with telluric lines for the strongly rotationally broadened primary lines (v sin(i) = 138 km s −1 ) to obtain radial velocities with an accuracy of a few hundred m/s. We combined our new RV data with older measurements, dating back to 1908 in the case of the primary, to search for evidence of apsidal motion. We find an apsidal motion period between 6600 and 10 600 yr. This value is consistent with the available data for both the primary and secondary and is also consistent with the assumption that the system has aligned orbit and rotation axes.

Section: Observations and Data Analysismentioning

confidence: 99%

TheαCrB binary system: A new radial velocity curve, apsidal motion, and the alignment of rotation and orbit axes

Schröder

Rauw

et al. 2016

A&A

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“…TIGRE is a 1.2 m robotic telescope, located in central Mexico and equipped with an echelle spectrograph with a nominal resolution of 20 000; for further details about the instrument and telescope we refer to Schmitt et al (2014). The raw data was reduced with the TIGRE reduction pipeline in version 2, which is based on the REDUCE package described in detail by Piskunov & Valenti (2002).…”

Section: Observations and Data Analysismentioning

confidence: 99%

On the nature of absorption features toward nearby stars

Kohl

Czesla

2016

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Context. Diffuse interstellar absorption bands (DIBs) of largely unknown chemical origin are regularly observed primarily in distant early-type stars. More recently, detections in nearby late-type stars have also been claimed. These stars' spectra are dominated by stellar absorption lines. Specifically, strong interstellar atomic and DIB absorption has been reported in τ Boo. Aims. We test these claims by studying the strength of interstellar absorption in high-resolution TIGRE spectra of the nearby stars τ Boo, HD 33608, and α CrB. Methods. We focus our analysis on a strong DIB located at 5780.61 Å and on the absorption of interstellar Na. First, we carry out a differential analysis by comparing the spectra of the highly similar F-stars, τ Boo and HD 33608, whose light, however, samples different lines of sight. To obtain absolute values for the DIB absorption, we compare the observed spectra of τ Boo, HD 33608, and α CrB to PHOENIX models and carry out basic spectral modeling based on Voigt line profiles. Results. The intercomparison between τ Boo and HD 33608 reveals that the difference in the line depth is 6.85 ± 1.48 mÅ at the DIB location which is, however, unlikely to be caused by DIB absorption. The comparison between PHOENIX models and observed spectra yields an upper limit of 34.0 ± 0.3 mÅ for any additional interstellar absorption in τ Boo; similar results are obtained for HD 33608 and α CrB. For all objects we derive unrealistically large values for the radial velocity of any presumed interstellar clouds. In τ Boo we find Na D absorption with an equivalent width of 0.65 ± 0.07 mÅ and 2.3 ± 0.1 mÅ in the D 2 and D 1 lines. For the other Na, absorption of the same magnitude could only be detected in the D 2 line. Our comparisons between model and data show that the interstellar absorption toward τ Boo is not abnormally high. Conclusions. We find no significant DIB absorption in any of our target stars. Any differences between modeled and observed spectra are instead attributable to inaccuracies in the stellar atmospheric modeling than to DIB absorption.

“…As far as τ Boo is concerned, Shkolnik et al (2008) present Ca II K data and argue that these data may indicate SPI, however, it is probably fair to say that actual observational clear-cut demonstrations of SPI are still very elusive. Mittag et al (2017) describe an S-index variability of τ Boo with a timescale of about 120 days observed in the years 2013-2016 with the TIGRE facility (Schmitt et al 2014) and show that the same period is also consistent with cyclic variability at X-ray wavelengths. Similarly, Mengel et al (2016), using their S-index time series taken with the NARVAL instrument in the years 2007-2015, deduce a 117-day period; we identify this period with the 116-day period previously mentioned, but not described by Baliunas et al (1997).…”

Section: Introductionmentioning

confidence: 65%

Further evidence for a sub-year magnetic chromospheric activity cycle and activity phase jumps in the planet hostτBoötis

Mittag

2017

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We examine the S-index data, obtained in the context of the Mount Wilson H&K project for the nearby F-type star τ Boo, for the presence of possible cyclic variations on timescales below one year and "phase jump" episodes in the observed S-index activity levels, to determine whether such features are persistent properties of the chromospheric activity of τ Boo and possibly other late-type stars. Within the Mount Wilson H&K project τ Boo was observed during 1278 individual nights, albeit with a very inhomogeneous coverage ranging from 2 to 137 observations per year. Our analysis shows that periodical variations with timescales on the order of 110-120 days are a persistent feature of the Mount Wilson data set. Furthermore we provide further examples of "phase jump" episodes, when the observed S-index activity drops from maximum to minimum levels on timescales of one to two weeks, hence such features also appear to occur on a more or less regular basis in τ Boo.