Hα ACTIVITY OF OLD M DWARFS: STELLAR CYCLES AND MEAN ACTIVITY LEVELS FOR 93 LOW-MASS STARS IN THE SOLAR NEIGHBORHOOD

Robertson, Paul; Endl, Michael; Cochran, William D.; Dodson-Robinson, Sarah

doi:10.1088/0004-637x/764/1/3

Cited by 110 publications

(132 citation statements)

References 63 publications

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“…We find evidence for rotation periods of the order of 10-40 days and active regions lifetime cycles longer than ≃50 days. These findings are in agreement with previous results (Donahue et al 1997a,b;Reiners et al 2012;Robertson et al 2013) and are supported by a more detailed analysis we are currently preparing (Suárez Mascareño et al 2016, in prep …”

Section: Discussionsupporting

confidence: 93%

“…9 for an example). Robertson et al (2013) found similar evidence analyzing the ∼11-year long series of Hα observations of a sample of 93 M-type dwarfs, and concluded that ∼10% of M dwarfs show either long-term trends or 1 year activity cycles.…”

Section: Ca II Handk Vs Hαmentioning

confidence: 59%

“…The PV then levels off at τ ∼50-60 days, suggesting that the new source of variance typically has time scales of a few stellar rotations. We exclude that the second flattening is due to cyclic activity for two reasons: as a matter of fact, dynamo cycles of M dwarfs act on year-long timescales, as indicated by Robertson et al (2013), and their effects should be greatly reduced due to the long-term correction we applied in Sect. 4.2.…”

Section: Variability Timescalesmentioning

confidence: 99%

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HADES RV Programme with HARPS-N at TNG

Scandariato

Maldonado

Affer

et al. 2017

A&A

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Context. M dwarfs are prime targets for current and future planet search programs, particularly of those focused on the detection and characterization of rocky planets in the habitable zone. In this context, understanding their magnetic activity is important for two main reasons: it affects our ability to detect small planets, and it plays a key role in the characterization of the stellar environment.Aims. We aim to analyze observations of the Ca ii H&K and Hα lines as diagnostics of chromospheric activity for low-activity early-type M dwarfs. Methods. We analyze the time series of spectra of 71 early-type M dwarfs collected in the framework of the HADES project for planet search purposes. The HARPS-N spectra provide simultaneously the Ca ii H&K doublet and the Hα line. We develop a reduction scheme able to correct the HARPS-N spectra for instrumental and atmospheric effects, and to provide also flux-calibrated spectra in units of flux at the stellar surface. The Ca ii H&K and Hα fluxes are then compared with each other, and their time variability is analyzed. Results. We find that the Ca ii H and K flux excesses are strongly correlated with each other, while the Hα flux excess is generally less correlated with the Ca ii H&K doublet. We also find that Hα emission does not increase monotonically with the Ca ii H&K line flux, showing some absorption before being filled in by chromospheric emission when Ca ii H&K activity increases. Analyzing the time variability of the emission fluxes, we derive a tentative estimate of the rotation period (of the order of a few tens of days) for some of the program stars, and the typical lifetime of chromospheric active regions (of the order of a few stellar rotations). Conclusions. Our results are in good agreement with similar previous studies. In particular, we find evidence that the chromospheres of early-type M dwarfs could be characterized by different filaments coverage, affecting the formation mechanism of the Hα line. We also show that chromospheric structure is likely related to spectral type.

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Section: Discussionsupporting

confidence: 93%

Section: Ca II Handk Vs Hαmentioning

confidence: 59%

Section: Variability Timescalesmentioning

confidence: 99%

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HADES RV Programme with HARPS-N at TNG

Scandariato

Maldonado

Affer

et al. 2017

A&A

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“…The spectroscopic activity diagnostics, namely the Full Width Half Maximum (FWHM) of the CCF, the ¢ R log HK index (Lovis et al 2011), and the Hα index (Gomes da Silva et al 2011;Robertson et al 2013), however, did not confirm this result, all suggesting instead a main periodicity around 14 days ( Figure 2). The auto correlation function on the K2 data, computed as described in McQuillan et al (2013) 36 also converged to 14 days.…”

Section: Stellar Activitymentioning

confidence: 95%

An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141

et al. 2018

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Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51±0.05R Å and a mass of 5.08±0.41M Å , consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30±0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ∼3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios.

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“…The Ca ii H&K lines are commonly used as optical activity proxies (e.g. Baliunas & Jastrow 1990;Baliunas et al 1998;Hall et al 2007), as are other lines, such as those of the Balmer series (Robertson et al 2013a;Reiners et al 2012) or the Mg ii infrared triplet (see e.g. Busà et al 2007;Pietarila & Livingston 2011).…”

Section: Introductionmentioning

confidence: 99%

Discovery of an activity cycle in the solar analog HD 45184

Flores

González

Arancibia

et al. 2016

A&A

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Context. Most stellar activity cycles similar to that found in the Sun have been detected by using the chromospheric Ca ii H&K lines as stellar activity proxies. However, it is unclear whether such activity cycles can be identified using other optical lines. Aims. We aim to detect activity cycles in solar-analog stars and determine whether they can be identified through other optical lines, such as Fe II and Balmer lines. We study the solar-analog star HD 45184 using HARPS spectra. The temporal coverage and high quality of the spectra allow us to detect both long-and short-term activity variations. Methods. We analysed the activity signatures of HD 45184 by using 291 HARPS spectra obtained between 2003 and 2014. To search for line-core flux variations, we focused on Ca ii H&K and Balmer Hα and Hβ lines, which are typically used as optical chromospheric activity indicators. We calculated the HARPS-S index from Ca ii H&K lines and converted it into the Mount Wilson scale. In addition, we also considered the equivalent widths of Balmer lines as activity indicators. Moreover, we analysed the possible variability of Fe ii and other metallic lines in the optical spectra. The spectral variations were analysed for periodicity using the Lomb-Scargle periodogram. Results. We report for the first time a long-term 5.14-yr activity cycle in the solar-analog star HD 45184 derived from Mount Wilson S index. This makes HD 45184 one of most similar stars to the Sun with a known activity cycle. The variation is also evident in the first lines of the Balmer series, which do not always show a correlation with activity in solar-type stars. Notably, unlike the solar case, we also found that the equivalent widths of the high photospheric Fe ii lines (4924 Å, 5018 Å and 5169 Å) are modulated (±2 mÅ) by the chromospheric cycle of the star. These metallic lines show variations above 4σ in the rms spectrum, while some Ba ii and Ti ii lines present variations at 3σ level, which could be considered as marginal variations. From short-term modulation of the S index we calculate a rotational period of 19.98 days, which agrees with its mean chromospheric activity level. We also clearly show that the activity cycles of HD 45184 can be detected in both Fe ii and Balmer lines.

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Hα ACTIVITY OF OLD M DWARFS: STELLAR CYCLES AND MEAN ACTIVITY LEVELS FOR 93 LOW-MASS STARS IN THE SOLAR NEIGHBORHOOD

Cited by 110 publications

References 63 publications

HADES RV Programme with HARPS-N at TNG

HADES RV Programme with HARPS-N at TNG

An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141

Discovery of an activity cycle in the solar analog HD 45184

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