J/A+A/704/A8 Observing log of individual spectra (Strassmeier+, 2025)
Surface activity of a Rossby sequence of cool Hyades stars.
Strassmeier K.G., Ilyin I., Steffen M., Barnes S.A.
<Astron. Astrophys. 704, A8 (2025)>
=2025A&A...704A...8S 2025A&A...704A...8S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, late-type ; Magnetic fields
Keywords: stars: activity - stars: magnetic field - stars: rotation -
starspots - open clusters and associations: individual: Hyades
Abstract:
The Hyades cluster is key for the study of rotational, activity, and
chemical evolution of solar-like low-mass stars. Here we present
quantitative surface-activity information for a sequence of 21 Hyades
dwarf stars with effective temperatures 6160K to 3780K (all cooler
than the red edge of the Li dip), rotation periods 5d to 16d and
normalized Rossby numbers (Ron) between 0.14 to 0.54 with respect to
the Sun (Ro(Sun)=1).
High-resolution Stokes-V spectra and least-squares deconvolution of
thousands of spectral lines per spectrum are employed for measuring
longitudinal surface magnetic field. From Stokes-I spectra we obtain
velocities, lithium abundances, metallicity, and chromospheric CaII
infrared-triplet (IRT) fluxes.
The average metallicity, +0.186±0.045 (rms), for our stars with
Teff≥4200K is in good agreement with the metallicity in the recent
literature. Lithium abundances A(Li) range from 95-times solar
(A(Li)~+3.0) on the warm end of the sample to 1/25 solar (A(Li)~-0.4)
on the cool end. We confirm the tight relation of A(Li) with Teff and
extend it to K-M stars with even smaller Li abundances than previously
measurable. A formal relation with rotational period and velocity in
the sense higher Li abundance for faster rotators is present. Targets
rotating faster than vsini of 6km/s (Prot∼8d) appear Li saturated at
A(Li)∼3.0dex. CaII IRT fluxes for our sample indicate (logarithmic)
chromospheric radiative losses RIRT in the range -4.0 to -4.9 in
units of the bolometric flux. These radiative losses also show a
relation with Teff, Prot, and vsini, but opposite to A(Li) in an
inverse sense with higher radiative losses for the slower=cooler
rotators. Longitudinal magnetic-field strengths were measured in the
range zero to -100G and +150G with phase-averaged, disk-integrated,
unsigned values <|B|> of 15.4±3.6(rms) G for targets warmer than
∼5000K and 91±61(rms)G for targets cooler than this. These unsigned
field strengths relate to Prot , vsini, and Ron, but in a dual-slope
fashion. The short-period bonafide single M-target RSP 348 was found
to be a double-lined spectroscopic binary of dM3e+dM5e classification.
We conclude that the Rossby-number dependencies of the surface
activity tracers A(Li), R'IRT , and <|B|> on our Hyades dwarf
sequence primarily originate from convective motions, expressed by its
turnover time, and only to a smaller and sometimes inverse extent from
surface rotation and its related extra mixing.
Description:
Observing log of individual spectra. The table consists of 9 columns.
First column is the target identification. Next two columns are the UT
date and UT start time of the first of the two CP integrations. Column
texp is the sum for both CP exposures. The next pair of columns is for
the blue (CD3) and red (CD5) cross dispersers, respectively, and
consist of column CD identifier and S/N. S/N is given for the sum
(Stokes-I) and are always per pixel for the 95% quantile. Column Phase
is given for the mid time of the two individual CP exposures.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 31 22 List of studied stars
tablec2.dat 77 300 Observing log of individual spectra
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Target Target name
9- 10 I2 h RAh Simbad right ascension (J2000)
12- 13 I2 min RAm Simbad right ascension (J2000)
15- 19 F5.2 s RAs Simbad right ascension (J2000)
21 A1 --- DE- Simbad declination sign (J2000)
22- 23 I2 deg DEd Simbad declination (J2000)
25- 26 I2 arcmin DEm Simbad declination (J2000)
28- 31 F4.1 arcsec DEs Simbad declination (J2000)
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Target Target name
9- 18 A10 "date" Date UT date of the first of the two CP integrations
20- 29 A10 "h:m:s" Tstart UT start of the first of the two CP integrations
31- 38 A8 "h:m:s" texp Sum for both CP exposures
40- 50 A11 --- CD3 Blue cross disperser identifier, CD: Delta-lambda
52- 54 I3 --- S/N3 Blue cross disperser signal-to-noise ratio
56- 66 A11 --- CD5 Red cross disperser identifier, CD: Delta-lambda
68- 71 I4 --- S/N5 Red cross disperser signal-to-noise ratio
73- 77 F5.3 --- Phase Phase for the mid time of the two individual
CP exposures
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Acknowledgements:
Klaus G. Strassmeier, kstrassmeier(at)aip.de
(End) Patricia Vannier [CDS] 28-Oct-2025