The au-scale structure in diffuse molecular gas towards<i>ζ</i> Persei

Boissé, Patrick; Federman, S. R.; Forêts, G. Pineau des; Ritchey, Adam M.

doi:10.1051/0004-6361/201322562

Cited by 8 publications

(7 citation statements)

References 42 publications

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“…On the one hand, within time-scales of tens of years, the ISM absorption can be considered to be stable (e.g. Boissé et al 2013), hence it does not introduce spurious variability that may interfere with planet detections. On the other hand, ISM absorption dims the stellar activity signal, up to the point where it may mask the Ca ii line core variability, leading to a mis-or non-detection of periodicities connected to stellar rotation and activity cycles, though they may be clearly present in the periodograms obtained from analysing the radial velocity measurements.…”

Section: Relevance For Exoplanet Studiesmentioning

confidence: 99%

The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

Fossati

Marcelja

Staab

et al. 2017

A&A

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Past ultraviolet and optical observations of stars hosting close-in Jupiter-mass planets have shown that some of these stars present an anomalously low chromospheric activity, significantly below the basal level. For the hot Jupiter planet host WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening interstellar medium (ISM). Inspired by this result, we study the effect of ISM absorption on activity measurements (S and log R ′ HK indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental (spectral resolution), stellar (projected rotational velocity, effective temperature, and chromospheric emission flux), and ISM parameters (relative velocity between stellar and ISM Ca ii lines, broadening b-parameter, and Ca ii column density). We find that for relative velocities between the stellar and ISM lines smaller than 30-40 km s −1 and for ISM Ca ii column densities log N CaII 12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM Ca ii column density of log N CaII = 12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the log R ′ HK value larger than 0.05-0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies and revise the latest results on stellar activity versus planet surface gravity correlation. We finally describe methods with which it would be possible to account for ISM absorption in activity measurements and provide a code to roughly estimate the magnitude of the bias. Correcting for the ISM absorption bias may allow one to identify the origin of the anomaly in the activity measured for some planet-hosting stars.

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Section: Relevance For Exoplanet Studiesmentioning

confidence: 99%

The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

Fossati

Marcelja

Staab

et al. 2017

A&A

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“…Such a technique applies from the solar neighbourhood towards nearby stars (e.g. Savage et al 1977;Boissé et al 2013) to the gas in and around high-redshift galaxies revealed by damped Lyman-α systems (DLAs; e.g. Levshakov et al 1989;Ge et al 1997;Petitjean et al 2000;Cui et al 2005;Srianand et al 2005;Noterdaeme et al 2008;Jorgenson et al 2010;Carswell et al 2011;Balashev et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Spotting high-z molecular absorbers using neutral carbon

Noterdaeme

Ledoux

Zou

et al. 2018

A&A

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While molecular quasar absorption systems provide unique probes of the physical and chemical properties of the gas as well as original constraints on fundamental physics and cosmology, their detection remains challenging. Here we present the results from a complete survey for molecular gas in thirty-nine absorption systems selected solely upon the detection of neutral carbon lines in Sloan Digital Sky Survey (SDSS) spectra, without any prior knowledge of the atomic or molecular gas content. H 2 is found in all twelve systems (including seven new detections) where the corresponding lines are covered by the instrument setups and measured to have log N(H 2 ) 18, indicating a self-shielded regime. We also report seven CO detections (7/39) down to log N(CO) ∼ 13.5, including a new one, and put stringent constraints on N(CO) for the remaining 32 systems. N(CO) and N(C I) are found to be strongly correlated with N(CO)/N(C I) ∼ 1/10. This suggests that the C I-selected absorber population is probing gas deeper than the H I-H 2 transition in which a substantial fraction of the total hydrogen in the cloud is in the form of H 2 . We conclude that targeting C I-bearing absorbers is a very efficient way to find high-metallicity molecular absorbers. However, probing the molecular content in lower-metallicity regimes as well as high-column-density neutral gas remains to be undertaken to unravel the processes of gas conversion in normal high-z galaxies.

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“…These observations imply a population of dense au-scale clouds in the ISM or changes in ionization or depletion over time, but are restricted to trace neutral species. Boissé et al (2013) studied the spatial distribution of CH + , CH and CN on scales ranging 1-20 au for a single sightline towards Zeta Per, finding the neutral species to be uniformly distributed and a CH + excess implying its production in very small localized active regions of only a few au. Data for UV absorption-lines can probe dominant ions and provide further information on the physical conditions; time-variable UV lines have been found by e.g.…”

Section: Introductionmentioning

confidence: 99%

Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

McEvoy

Smoker

Dufton

et al. 2015

Monthly Notices of the Royal Astronomical Society

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The structure and properties of the diffuse interstellar medium (ISM) on small scales, sub-au to 1 pc, are poorly understood. We compare interstellar absorption-lines, observed towards a selection of O-and B-type stars at two or more epochs, to search for variations over time caused by the transverse motion of each star combined with changes in the structure in the foreground ISM. Two sets of data were used: 83 VLT-UVES spectra with approximately 6 yr between epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 -20 yr between epochs, over a range of scales from ∼ 0 -360 au. The interstellar absorption-lines observed at the two epochs were subtracted and searched for any residuals due to changes in the foreground ISM. Of the 104 sightlines investigated with typically five or more components in Na i D, possible temporal variation was identified in five UVES spectra (six components), in Ca ii, Ca i and/or Na i absorption-lines. The variations detected range from 7% to a factor of 3.6 in column density. No variation was found in any other interstellar species. Most sightlines show no variation, with 3σ upper limits to changes of the order 0.1 -0.3 dex in Ca ii and Na i. These variations observed imply that fine-scale structure is present in the ISM, but at the resolution available in this study, is not very common at visible wavelengths. A determination of the electron densities and lower limits to the total number density of a sample of the sightlines implies that there is no striking difference between these parameters in sightlines with, and sightlines without, varying components.

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The au-scale structure in diffuse molecular gas towardsζ Persei

Cited by 8 publications

References 42 publications

The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

Spotting high-z molecular absorbers using neutral carbon

Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

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