J/A+A/689/A241 Photometry and RVs of BL Her stars (Wielgorski+, 2024)
Projection factor and radii of Type II Cepheids. BL Her stars.
Wielgorski P., Pietrzynski G., Gieren W., Zgirski B., Gorski M., Storm J.,
Nardetto N., Kervella P., Bras G., Hajdu G., Hocde V., Pilecki B.,
Narloch W., Karczmarek P., Pych W., Chini R., Hodapp K.
<Astron. Astrophys. 689, A241 (2024)>
=2024A&A...689A.241W 2024A&A...689A.241W (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Stars, variable ; Photometry ; Optical ;
Radial velocities
Keywords: stars: distances - stars: Population II - stars: variables: Cepheids
Abstract:
Type II Cepheids are old pulsating stars that can be used to trace the
distribution of an old stellar population and to measure distances to
globular clusters and galaxies within several megaparsecs, and by
extension, they can improve our understanding of the cosmic distance
scale. One method that can be used to measure the distances of Type II
Cepheids relies on period-luminosity relations, which are quite widely
explored in the literature. The semi-geometrical Baade-Wesselink
technique is another method that allows distances of radially
pulsating stars, such as Type II Cepheids, to be measured if the
so-called projection factor is known. However, the literature
concerning this parameter for Type II Cepheids is limited to just a
few pioneering works.
In determining projection factors for eight nearby short-period Type
II Cepheids, also known as BL Her type stars, we aim to calibrate the
Baade-Wesselink method for measuring distances for this class of
stars.
Using the surface brightness-colour relation version of the
Baade-Wesselink technique, we determined the projection factors and
radii of eight nearby BL Her type stars. We adopted accurate distances
of target stars from Gaia Data Release 3. Time series photometry in
the V and KS bands have been collected with two telescopes located at
the Rolf Chini Cerro Murphy Observatory (former Cerro Armazones
Observatory), while spectroscopic data have been obtained within
dedicated programmes with instruments hosted by the European Southern
Observatory.
The measured projection factors for the stars with good quality data
are in the range between 1.21 and 1.36. The typical uncertainty of
projection factors is 0.1. The mean value is 1.330±0.058, which
gives the uncertainty of ∼4%. The main sources of uncertainty on the
p-factors are statistical errors of the Baade-Wesselink fit (related
to the dispersion and coverage of light and radial velocity curves)
and parallax. In the case of radii, the biggest contribution to the
error budget comes from the Ks band photometry's systematic
uncertainty and parallax. The determined radii allowed us to construct
the period-radius relation for BL Her stars. Our period-radius
relation is in good agreement with the previous empirical calibration,
while two theoretical calibrations found in the literature agree with
our relation within 2σ. We also confirm that BL Her and RR Lyr
stars obey an apparent common period-radius relation.
Description:
Optical photometry in the Johnson B and V passbands were obtained with
the VYSOS16 0.4-metre telescope located at Rolf Chini Cerro Murphy
Observatory (Ramolla et al. 2013) with a pixel scale of 0.77arcsec/pix
and a 41.2'x25.5' field of view.
Radial velocities were measured from spectra collected between 2016
and 2023 within dedicated programmes with four high resolution
(40000-100000) spectrographs hosted by the European Southern
Observatory (ESO). We used CORALIE, installed on the 1.2m 'Swiss'
Leonhard Euler telescope at La Silla Observatory (Queloz et al.
2000); HARPS, installed on the 3.6m telescope at La Silla
Observatory (Pepe et al. 2000); FEROS, installed on the 2.2m MPG/ESO
telescope at La Silla Observatory (Kaufer & Pasquini 1998); and
UVES, installed on the 8.2m VLT UT2 (Kueyen) telescope at the Paranal
Observatory (D'Odorico et al. 2000, SPIE Conf. Ser., 4005, 121,
filler programme).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 61 8 Data of Type II Cepheids
table1.dat 38 403 Optical photometry of Type II Cepheids
table3.dat 64 331 Radial velocities of Type II Cepheids
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Star name
10- 17 F8.6 d Per Period
19- 24 F6.4 mas plx Parallax
26- 31 F6.4 mas e_plx Parallax error
33- 39 F7.4 mas ZPO Parallax zero-point offset
41- 45 F5.2 mag Gmag Gaia G-band magnitude
47- 50 F4.2 mag Bp-Rp Gaia Bp-Rp color index
52- 56 F5.3 mag E(B-V) E(B-V) color excess
58- 61 F4.2 mag e_E(B-V) E(B-V) color excess error
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Star name
10 A1 --- Filter [BV] Name of the photometric filter
12- 25 F14.6 d HJD Heliocentric Julian Date
27- 32 F6.3 mag mag Magnitude of the star in Filter
34- 38 F5.3 mag e_mag Magnitude error of the star in Filter
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Star name
10- 27 F18.10 d HJD Heliocentric Julian date
29- 35 F7.2 km/s RVg Radial velocity measured with CCF modelled
with Gaussian profile
37- 40 F4.2 km/s e_RV Uncertainy of radial velocity measurement
42- 48 F7.2 km/s RVc ?=- Radial velocity measured with CCF from centroid
50- 56 F7.2 km/s RVb Radial velocity measured with CCD modelled
with bi-Gaussian profile
58- 64 A7 --- Inst Instrument used to obtain the spectrum
--------------------------------------------------------------------------------
Acknowledgements:
Piotr Wielgorski, pwielgor(at)camk.edu.pl
(End) Patricia Vannier [CDS] 24-Jun-2024