An investigation of chromospheric
 activity spanning   the Vaughan-Preston gap: impact on stellar ages

AbstractEarth is the only planet known to harbor life, therefore we may speculate on how the nature of the Sun-Earth interaction is relevant to life on Earth, and how the behavior of other stars may influence the development of life on their planetary systems. We study the long-term variability of a sample of five solar analog stars using composite chromospheric activity records up to 50 years in length and synoptic visible-band photometry about 20 years long. This sample covers a large range of stellar ages which we use to represent the evolution in activity for solar mass stars. We find that young, fast rotators have an amplitude of variability many times that of the solar cycle, while old, slow rotators have very little variability. We discuss the possible impacts of this variability on young Earth and exoplanet climates.

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Chromospheric activity as a function of age in main-sequence stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900053146 ◽

1966 ◽

Vol 24 ◽

pp. 40-43

Author(s):

O. C. Wilson ◽

A. Skumanich

Keyword(s):

Main Sequence ◽

The Sun ◽

Main Sequence Stars ◽

Tentative Conclusion ◽

Chromospheric Activity ◽

General Field ◽

Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

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Realistic mock observations of the sizes and stellar mass surface densities of massive galaxies in FIRE-2 zoom-in simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3765 ◽

2020 ◽

Vol 501 (2) ◽

pp. 1591-1602

Author(s):

T Parsotan ◽

R K Cochrane ◽

C C Hayward ◽

D Anglés-Alcázar ◽

R Feldmann ◽

...

Keyword(s):

Galaxy Formation ◽

Surface Density ◽

Stellar Mass ◽

Massive Galaxies ◽

Star Forming ◽

Stellar Feedback ◽

Central Surface ◽

Stellar Ages ◽

The Galaxy ◽

Zoom In

ABSTRACT The galaxy size–stellar mass and central surface density–stellar mass relationships are fundamental observational constraints on galaxy formation models. However, inferring the physical size of a galaxy from observed stellar emission is non-trivial due to various observational effects, such as the mass-to-light ratio variations that can be caused by non-uniform stellar ages, metallicities, and dust attenuation. Consequently, forward-modelling light-based sizes from simulations is desirable. In this work, we use the skirt dust radiative transfer code to generate synthetic observations of massive galaxies ($M_{*}\sim 10^{11}\, \rm {M_{\odot }}$ at z = 2, hosted by haloes of mass $M_{\rm {halo}}\sim 10^{12.5}\, \rm {M_{\odot }}$) from high-resolution cosmological zoom-in simulations that form part of the Feedback In Realistic Environments project. The simulations used in this paper include explicit stellar feedback but no active galactic nucleus (AGN) feedback. From each mock observation, we infer the effective radius (Re), as well as the stellar mass surface density within this radius and within $1\, \rm {kpc}$ (Σe and Σ1, respectively). We first investigate how well the intrinsic half-mass radius and stellar mass surface density can be inferred from observables. The majority of predicted sizes and surface densities are within a factor of 2 of the intrinsic values. We then compare our predictions to the observed size–mass relationship and the Σ1−M⋆ and Σe−M⋆ relationships. At z ≳ 2, the simulated massive galaxies are in general agreement with observational scaling relations. At z ≲ 2, they evolve to become too compact but still star forming, in the stellar mass and redshift regime where many of them should be quenched. Our results suggest that some additional source of feedback, such as AGN-driven outflows, is necessary in order to decrease the central densities of the simulated massive galaxies to bring them into agreement with observations at z ≲ 2.

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The stellar mass assembly of low-redshift, massive, central galaxies in SDSS and the TNG300 simulation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2306 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4262-4275

Author(s):

Thomas M Jackson ◽

A Pasquali ◽

C Pacifici ◽

C Engler ◽

A Pillepich ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Stellar Mass ◽

Spectral Energy ◽

Distribution Fitting ◽

Stellar Ages ◽

Mass Assembly ◽

Galaxy Assembly ◽

The Times ◽

Stellar Masses ◽

Kinetic Mode

ABSTRACT The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim 90\, 000$ low-redshift, central galaxies selected from SDSS group catalogues ($M_{\rm Stellar}\gtrsim 10^{9.5}\, \mathrm{M}_{\odot }$, $M_{\rm Halo}\gtrsim 10^{12}\, \mathrm{M}_{\odot }$) as a function of both stellar mass and halo mass. We use estimates of the times at which 10, 50, and 90 per cent of the stellar mass were assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar mass and halo mass simultaneously, finding dependences of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a subsample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar mass or halo mass. However, some differences in the assembly times (of up to ∼3 Gyr) appear when considering both stellar mass and halo mass simultaneously, noticeably at intermediate stellar masses (MStellar ∼ 1011 M⊙). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode active galactic nucleus feedback implemented in TNG300.

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Chromospheric activity in several single late-type stars

Research in Astronomy and Astrophysics ◽

10.1088/1674-4527/15/2/009 ◽

2015 ◽

Vol 15 (2) ◽

pp. 252-274 ◽

Cited By ~ 3

Author(s):

Li-Yun Zhang ◽

Qing-Feng Pi ◽

Zhong-Zhong Zhu

Keyword(s):

Late Type ◽

Chromospheric Activity

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A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833315 ◽

2018 ◽

Vol 615 ◽

pp. L5 ◽

Cited By ~ 7

Author(s):

A. Irrgang ◽

S. Kreuzer ◽

U. Heber ◽

W. Brown

Keyword(s):

Main Sequence ◽

Galactic Center ◽

Radial Velocities ◽

Stellar Ages ◽

The Galaxy ◽

Quantitative Spectral Analysis ◽

Kinematic Studies ◽

Ejection Mechanism ◽

Photometric Measurements ◽

Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

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The onset of chromospheric activity among the A- and F- type stars

Cool Stars, Stellar Systems, and the Sun - Lecture Notes in Physics ◽

10.1007/3-540-18653-0_142 ◽

2008 ◽

pp. 265-268 ◽

Cited By ~ 5

Author(s):

Theodore Simon ◽

Wayne Landsman

Keyword(s):

Chromospheric Activity

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Masses and ages for metal-poor stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834081 ◽

2019 ◽

Vol 627 ◽

pp. A173 ◽

Cited By ~ 4

Author(s):

M. Valentini ◽

C. Chiappini ◽

D. Bossini ◽

A. Miglio ◽

G. R. Davies ◽

...

Keyword(s):

High Resolution ◽

Seismic Data ◽

Age Determination ◽

High Resolution Spectroscopy ◽

Chemical Abundances ◽

Abundance Pattern ◽

Halo Stars ◽

Stellar Ages ◽

First Results ◽

Detailed Chemical

Context. Very metal-poor halo stars are the best candidates for being among the oldest objects in our Galaxy. Samples of halo stars with age determination and detailed chemical composition measurements provide key information for constraining the nature of the first stellar generations and the nucleosynthesis in the metal-poor regime. Aims. Age estimates are very uncertain and are available for only a small number of metal-poor stars. We present the first results of a pilot programme aimed at deriving precise masses, ages, and chemical abundances for metal-poor halo giants using asteroseismology and high-resolution spectroscopy. Methods. We obtained high-resolution UVES spectra for four metal-poor RAVE stars observed by the K2 satellite. Seismic data obtained from K2 light curves helped improve spectroscopic temperatures, metallicities, and individual chemical abundances. Mass and ages were derived using the code PARAM, investigating the effects of different assumptions (e.g. mass loss and [α/Fe]-enhancement). Orbits were computed using Gaia DR2 data. Results. The stars are found to be normal metal-poor halo stars (i.e. non C-enhanced), and an abundance pattern typical of old stars (i.e. α and Eu-enhanced), and have masses in the 0.80−1.0 M⊙ range. The inferred model-dependent stellar ages are found to range from 7.4 Gyr to 13.0 Gyr with uncertainties of ∼30%−35%. We also provide revised masses and ages for metal-poor stars with Kepler seismic data from the APOGEE survey and a set of M4 stars. Conclusions. The present work shows that the combination of asteroseismology and high-resolution spectroscopy provides precise ages in the metal-poor regime. Most of the stars analysed in the present work (covering the metallicity range of [Fe/H] ∼ −0.8 to −2 dex) are very old >9 Gyr (14 out of 19 stars), and all of the stars are older than >5 Gyr (within the 68 percentile confidence level).

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The large scale magnetic field of the G0 dwarf HD 206860 (HN Peg)

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314001926 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 146-147

Author(s):

Sudeshna Boro Saikia ◽

Sandra V. Jeffers ◽

Pascal Petit ◽

Stephen Marsden ◽

Julien Morin ◽

...

Keyword(s):

Magnetic Field ◽

Spectral Type ◽

Large Scale ◽

Longitudinal Magnetic Field ◽

Chromospheric Activity ◽

Large Scale Magnetic Field ◽

Debris Disk ◽

Infrared Triplet

AbstractHD 206860 is a young planet (HN Peg b) hosting star of spectral type G0V and it has a potential debris disk around it. In this work we measure the longitudinal magnetic field of HD 206860 using spectropolarimetric data and we measure the chromospheric activity using Ca II H&K, H-alpha and Ca II infrared triplet lines.

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