J/A+A/691/A186 Spectra of 27 ssrAp star candidates (Mathys+, 2024)
Super-slowly rotating Ap (ssrAp) stars: Spectroscopic study.
Mathys G., Holdsworth D.L., Giarrusso M., Kurtz D.W., Catanzaro G., Leone F.
<Astron. Astrophys., 691, A186 (2024)>
=2024A&A...691A.186M 2024A&A...691A.186M (SIMBAD/NED BibCode)
+2025A&A...694C...7M 2025A&A...694C...7M
ADC_Keywords: Stars, Ap ; Spectra, optical
Keywords: binaries: spectroscopic - stars: chemically peculiar -
stars: magnetic field - stars: oscillations - stars: rotation
Abstract:
The fact that the rotation periods of Ap stars span five to six orders
of magnitude and that the longest ones reach several hundred years
represents one of the main unsolved challenges of stellar physics.
Our goal is to gain better understanding of the occurrence and
properties of the longest period Ap stars.
We obtained high resolution spectra of a sample of super-slowly
rotating Ap (ssrAp) star candidates identified by a TESS photometric
survey to confirm that they are indeed Ap stars, to check that their
projected equatorial velocities are compatible with super-slow
rotation, and to obtain a first estimate of their magnetic field
strengths. For the confirmed Ap stars, we determined whenever possible
their mean magnetic field modulus, their mean quadratic magnetic
field, and an upper limit of their projected equatorial velocities.
Eighteen of the 27 stars studied are typical Ap stars; most of the
other nine appear to be misclassified. One of the Ap stars is not a
slow rotator; it must be seen nearly pole-on. The properties of the
remaining 17 are compatible with moderately to extremely long rotation
periods. Eight new stars with resolved magnetically split lines in the
visible range were discovered; their mean magnetic field modulus and
their mean quadratic magnetic field were measured. The mean quadratic
field could also be determined in five more stars. Five spectroscopic
binaries containing an Ap star, which were not previously known, were
identified. Among the misclassified stars, one double-lined
spectroscopic binary with two similar, sharp-lined Am components was
also discovered.
The technique that we used to carry out a search for ssrAp star
candidates using TESS data is validated. Its main limitation appears
to arise from uncertainties in the spectral classification of Ap
stars. The new magnetic field measurements obtained as part of this
study lend further support to the tentative conclusions of our
previous studies: the absence of periods Prot≳150d in stars with
B0≳7.5kG, the lower rate of occurrence of super-slow rotation for
field strengths B0≲2kG than in the range ∼3kG<B0≲7.5kG, and the
deficiency of slowly rotating Ap stars with (phase-averaged) field
strengths between ∼2 and ∼3kG.
Description:
The reduced, normalised spectra of 27 super-slowly rotating Ap (ssrAp)
stars identified from a TESS photometric survey are presented. These
spectra were used to confirm that the studied stars are indeed Ap
stars, to check that their projected equatorial velocities are
compatible with super-slow rotation, and to obtain a first estimate of
their magnetic field strengths. For the corresponding measurements, a
local continuum was defined for each spectral line. Accordingly, the
overall normalisation of the whole spectrum may only be approximate,
hence unsuitable for some purposes (for instance, characterisation of
the hydrogen Balmer line profiles). The file summary below gives for
each spectrum the star ID in the TESS Input Catalogue (TIC), the
Julian Date of the observation, and the spectrograph that was used:
HARPS-N at the Telescopio Nazionale Galileo, HRS at the South African
Large Telescope (SALT), CAOS at the 0.9-m telescope of the Catania
Astrophysical Observatory, FEROS at the 2.2-m telescope of the
European Southern Observatory, or ESPaDOnS at the Canada-France-Hawaii
Telescope.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 37 25 List of studied stars
listsp.dat 48 54 List of spectra
sp/* . 54 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- 13 A13 --- Star Star name (TIC NNNNNNNNN)
15- 16 I2 h RAh Simbad right ascension (J2000)
18- 19 I2 min RAm Simbad right ascension (J2000)
21- 25 F5.2 s RAs Simbad right ascension (J2000)
27 A1 --- DE- Simbad declination sign (J2000)
28- 29 I2 deg DEd Simbad declination (J2000)
31- 32 I2 arcmin DEm Simbad declination (J2000)
34- 37 F4.1 arcsec DEs Simbad declination (J2000)
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Byte-by-byte Description of file: listsp.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Star Star name (TIC NNNNNNNNN)
15- 23 F9.1 d JD Observation Julian date
25- 32 A8 --- Inst Instrument
35- 48 A14 --- FileName Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.4 0.1nm lambda Wavelength in heliocentric reference frame (1)
13- 21 F9.4 --- Flux Flux normalised to continuum
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Note (1): The FEROS spectra represent an exception, with the
wavelength approximately in the laboratory reference frame.
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Acknowledgements:
Gautier Mathys, gmathys(at)eso.org
(End) Gautier Mathys [ESO, Chile], Patricia Vannier [CDS] 22-Jan-2025