J/MNRAS/483/5026 Radial velocities of Hyades stars (Leao+, 2019)
Spectroscopic and astrometric radial velocities: Hyades as a benchmark.
Leao I.C., Pasquini L., Ludwig H.-G., de Medeiros J.R.
<Mon. Not. R. Astron. Soc., 483, 5026-5041 (2019)>
=2019MNRAS.483.5026L 2019MNRAS.483.5026L (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, late-type ; Radial velocities ;
Positional data ; Optical
Keywords: open clusters and associations: individual: Hyades -
stars: late-type - techniques: radial velocities - Astrometry
Abstract:
We study the accuracy of spectroscopic radial velocities (RVs) by
comparing spectroscopic and astrometric RVs for stars of the Hyades
open cluster. We obtained High-Accuracy Radial velocity Planet
Searcher (HARPS) spectra for a large sample of Hyades stars and
combined them with accurate astrometric RVs based on Hipparcos and
Gaia data. After cleaning the sample from binaries, RV variables, and
outliers, 71 stars remained. The distribution of the observed RV
difference (between spectroscopic and astrometric) is skewed and
depends on the star right ascension. This is consistent with the
Hyades cluster rotating at 42.3m/s/pc. The two Hyades giants in the
sample show, as predicted by gravitational redshift (GR), a
spectroscopic RV that is blue-shifted with respect to the dwarfs, and
the empirical GR slope is of 626±131m/s, in agreement with the
theoretical prediction. The difference between spectroscopic and
astrometric RVs is close to zero when considering the Gaia-based RVs
corrected for cluster rotation. The mean difference is of -33m/s and
the median is of -16m/s, with a standard deviation of 347m/s being
close to the expected cluster velocity dispersion. We also determine a
new value of the cluster centroid spectroscopic RV: 39.36±0.26km/s.
We finally discuss other phenomena that can influence the RV
difference, such as cluster expansion, stellar rotation, stellar
activity, general relativity, and Galactic potential. Clusters within
the reach of current telescopes are expected to show differences of
several hundreds m/s, depending on their position in the Galaxy.
Description:
The Hyades is a relatively young cluster, with an age of ∼625±50Myr
(Perryman et al. 1998A&A...331...81P 1998A&A...331...81P, Cat. J/A+A/331/81, P98), and it
is the closest open cluster to the Sun (∼46.5pc; van Leeuwen
2009A&A...497..209V 2009A&A...497..209V). For this work, we use as a baseline the Madsen
et al. (2002A&A...381..446M 2002A&A...381..446M, Cat. J/A+A/381/446 , M02) study that
provided a clean sample, astrometric RVs for all stars and compared
them with the spectroscopic ones. A total of 218 stars, selected from
the list of P98, were observed, out of which 131 match with the list
of M02, which is cleaned for membership and some binarity.
All spectra were acquired with the HARPS (Mayor et al.
2003Msngr.114...20M 2003Msngr.114...20M) high-resolution spectrograph (R=115000), fed by
the 3.6m telescope in La Silla, Chile. The spectral range covers from
3800 to 6900Å, with a small gap between 5300 and 5330Å because
of the arrangement of the CCD mosaic. All the spectra were reprocessed
by the last version of the HARPS pipeline (Data Reduction Software
version 3.5). All stars have been observed once, in some case
observations have been repeated, if the first spectrum casted doubts
on the quality of the data. The S/N ratio was always exceeding 50 that
implies a photon noise precision of 2m/s or better for a slow rotating
G star; as explained above, photon noise is not limiting the accuracy
of the measurements. The list of the observed stars and the measured
RV is given in Table 1.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 101 131 Selected objects in the Hyades cluster
table2.dat 238 71 Gravitational and convective shifts
tablea1.dat 172 21 Cross-correlation results
tableb1.dat 50 65 Additional astrometric data
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/131] Internal object identifier
5- 13 A9 --- Name Hiparcos number (HIP NNNNN)
15- 21 A7 --- SpType Spectral type from the Hipparcos catalogue
23- 27 F5.2 mag Vmag Visual magnitude
29- 33 F5.3 mag B-V B-V colour index
35- 39 F5.3 mag e_B-V Error on B-V
41- 45 F5.2 km/s RVP98 Spectroscopic radial velocity from
Perryman et al. 1998A&A...331...81P 1998A&A...331...81P,
Cat. J/A+A/331/81 (P98)
47- 50 F4.2 km/s e_RVP98 Error on RVP98
52- 56 F5.2 km/s RVM02 Astrometric radial velocity from
Madsen et al. 2002A&A...381..446M 2002A&A...381..446M,
Cat. J/A+A/381/446 (M02)
58- 61 F4.2 km/s e_RVM02 Error on RVM02
63- 67 F5.2 km/s RVG17 Astrometric radial velocity computed in this
work from Gaia DR1 data (Gaia Collaboration
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337)
69- 72 F4.2 km/s e_RVG17 Error on RVG17
74- 81 F8.4 km/s RVHarps HARPS radial velocity (1)
83- 88 F6.4 km/s e_RVHarps Error on RVHarps
90- 94 F5.1 km/s FWHM Full width at half-maximum of the HARPS CCF
96- 98 I3 --- S/N Signal to noise ratio at 490um
100-101 A2 --- q_RVHarps Quality flag on HARPS data (2)
--------------------------------------------------------------------------------
Note (1): Our HARPS radial velocity measurements without zero-point correction,
from which we subtracted the HARPS mask zero-point of 102m/s for our
analysis
Note (2): Quality flag as follows:
0 = Acceptable HARPS data with higher-quality CCF shape
1 = Acceptable HARPS data with lower-quality CCF shape
BY = BY Dra variables with acceptable CCF shape
SB = Spectroscopic binaries
x = Excluded targets (because of bad-quality CCF)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID Internal object identifier
4- 12 A9 --- Name Hiparcos number (HIP NNNNN)
14- 20 F7.4 deg RAdeg Right ascension (J2000) (1)
22- 28 F7.4 deg DEdeg Declination (J2000) (1)
30- 34 F5.3 Sun M/R Stellar mass to radius ratio
36- 40 F5.3 Sun e_M/R Error on M/R
42- 44 I3 m/s GR Gravitational redshift
46- 49 I4 m/s C Estimated convective shift
51- 54 I4 m/s GRC Gravitational plus convective shifts
56- 60 I5 m/s DRVM02 Radial velocity difference between HARPS
(without zero-point correction) and
Madsen et al. (2002A&A...381..446M 2002A&A...381..446M,
Cat. J/A+A/381/446) measurements
62- 66 I5 m/s DRVM02GR DRVM02 corrected for gravitational redshift
68- 72 I5 m/s DRVM02GRC DRVM02 corrected for gravitational plus
convective shifts
74- 78 I5 m/s DRVG17 Radial velocity difference between HARPS
(without zero-point correction) and
Gaia DR1 (Gaia collaboration,
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337)
measurements
80- 84 I5 m/s DRVG17GR DRVG17 corrected for gravitational redshift
86- 90 I5 m/s DRVG17GRC DRVG17 corrected for gravitational plus
convective shifts
92- 97 A6 --- SpType Spectral type from the Hipparcos catalogue
99-103 F5.2 mag Vmag Visual magnitude
105-109 F5.3 mag B-V B-V colour index
111-115 F5.3 mag e_B-V Error on B-V
117-121 F5.2 km/s RVP98 Spectroscopic radial velocity from
Perryman et al. 1998A&A...331...81P 1998A&A...331...81P,
Cat. J/A+A/331/81 (P98)
123-126 F4.2 km/s e_RVP98 Error on RVP98
128-132 F5.2 km/s RVM02 Astrometric radial velocity from
Madsen et al. 2002A&A...381..446M 2002A&A...381..446M,
Cat. J/A+A/381/446 (M02)
134-137 F4.2 km/s e_RVM02 Error on RVM02
139-143 F5.2 km/s RVG17 Astrometric radial velocity computed in
this work from Gaia DR1 data (Gaia
Collaboration 2017A&A...601A..19G 2017A&A...601A..19G,
Cat. I/337)
145-148 F4.2 km/s e_RVG17 Error on RVG17
150-156 F7.4 km/s RVHarps HARPS radial velocity (2)
158-163 F6.4 km/s e_RVHarps Error on RVHarps
165-168 F4.1 km/s FWHM Full width at half-maximum of the HARPS CCF
170-172 I3 --- S/N Signal to noise ratio at 490um
174-175 A2 --- q_RVHarps Quality flag on HARPS data (3)
177-181 F5.2 pc r-rc ? Distance from the cluster center
183-186 F4.2 pc e_r-rc ? Error on r-rc
188-193 F6.3 km/s Valpha ? Tangential component in the α
direction for the astrometric vectors
computed from Gaia DR1 (Gaia Collaboration
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337) (4)
195-199 F5.3 km/s e_Valpha ? Error on Valpha
201-207 F7.3 km/s Vdelta ? Tangential component in the δ
direction for the astrometric vectors
computed from Gaia DR1 (Gaia Collaboration
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337) (4)
209-213 F5.3 km/s e_Vdelta ? Error on Vdelta
215-218 I4 m/s CR Estimated cluster rotation effect
220-226 F7.4 m/s RVHGRC RVHarps corrected for gravitational plus
convective shifts
228-232 F5.2 m/s RVG17CR RVG17 corrected for cluster rotation effect
234-238 I5 m/s DRVG17GRCCR DRVG17 corrected for gravitational plus
convective shifts and cluster rotation
effect
--------------------------------------------------------------------------------
Note (1): Positions from Gaia DR1 (Gaia Collaboration 2017A&A...601A..19G 2017A&A...601A..19G,
Cat. I/337)
Note (2): Our HARPS radial velocity measurements without zero-point correction,
from which we subtracted the HARPS mask zero-point of 102m/s for our
analysis
Note (3): Quality flag as follows:
0 = Acceptable HARPS data with higher-quality CCF shape
1 = Acceptable HARPS data with lower-quality CCF shape
BY = BY Dra variables with acceptable CCF shape
SB = Spectroscopic binaries
x = Excluded targets (because of bad-quality CCF)
Note (4): The tangential components are given by Valpha=kµα*/π
and Vdelta=kµδ/π, where
µα*=µαcosδ and µδ are the
proper motions given in mas/yr, π is the parallax given in mas,
and k=4.74047 km.yr/s is the factor that transforms from au/yr to km/s
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- SpecID Synthetic spectra identifier
9- 12 I4 K Teff Effective temperature
14- 17 F4.2 [cm/s2] logg Surface gravity
19- 21 F3.1 km/s FWHM0.0 FWHM of the cross-correlation peak for
ξ=0.0km/s (1)
23- 25 F3.1 km/s FWHM1.0 FWHM of the cross-correlation peak for
ξ=1.0km/s (1)
27- 29 F3.1 km/s FWHM2.0 FWHM of the cross-correlation peak for
ξ=2.0km/s (1)
31- 33 F3.1 km/s FWHM2.44 FWHM of the cross-correlation peak for
ξ=2.44km/s (1)
35- 37 F3.1 km/s FWHM3.0 FWHM of the cross-correlation peak for
ξ=3.0km/s (1)
39- 42 F4.1 km/s FWHM4.0 FWHM of the cross-correlation peak for
ξ=4.0km/s (1)
44- 47 F4.1 km/s FWHM5.0 FWHM of the cross-correlation peak for
ξ=5.0km/s (1)
49- 52 F4.1 km/s FWHM6.0 FWHM of the cross-correlation peak for
ξ=6.0km/s (1)
54- 57 F4.1 km/s FWHM7.0 FWHM of the cross-correlation peak for
ξ=7.0km/s (1)
59- 62 F4.1 km/s FWHM8.0 FWHM of the cross-correlation peak for
ξ=8.0km/s (1)
64- 67 F4.1 km/s FWHM9.0 FWHM of the cross-correlation peak for
ξ=9.0km/s (1)
69- 72 F4.1 km/s FWHM10.0 FWHM of the cross-correlation peak for
ξ=10.0km/s (1)
74- 77 F4.1 km/s FWHM12.5 FWHM of the cross-correlation peak for
ξ=12.5km/s (1)
79- 82 F4.1 km/s FWHM15.0 FWHM of the cross-correlation peak for
ξ=15.0km/s (1)
84- 87 F4.1 km/s FWHM17.5 FWHM of the cross-correlation peak for
ξ=17.5km/s (1)
89- 92 F4.1 km/s FWHM20.0 FWHM of the cross-correlation peak for
ξ=20.0km/s (1)
94- 97 I4 m/s pos0.0 Position of the cross-correlation peak for
ξ=0.0km/s (1)
99-102 I4 m/s pos1.0 Position of the cross-correlation peak for
ξ=1.0km/s (1)
104-107 I4 m/s pos2.0 Position of the cross-correlation peak for
ξ=2.0km/s (1)
109-112 I4 m/s pos2.44 Position of the cross-correlation peak for
ξ=2.44km/s (1)
114-117 I4 m/s pos3.0 Position of the cross-correlation peak for
ξ=3.0km/s (1)
119-122 I4 m/s pos4.0 Position of the cross-correlation peak for
ξ=4.0km/s (1)
124-127 I4 m/s pos5.0 Position of the cross-correlation peak for
ξ=5.0km/s (1)
129-132 I4 m/s pos6.0 Position of the cross-correlation peak for
ξ=6.0km/s (1)
134-137 I4 m/s pos7.0 Position of the cross-correlation peak for
ξ=7.0km/s (1)
139-142 I4 m/s pos8.0 Position of the cross-correlation peak for
ξ=8.0km/s (1)
144-147 I4 m/s pos9.0 Position of the cross-correlation peak for
ξ=9.0km/s (1)
149-152 I4 m/s pos10.0 Position of the cross-correlation peak for
ξ=10.0km/s (1)
154-157 I4 m/s pos12.5 Position of the cross-correlation peak for
ξ=12.5km/s (1)
159-162 I4 m/s pos15.0 Position of the cross-correlation peak for
ξ=15.0km/s (1)
164-167 I4 m/s pos17.5 Position of the cross-correlation peak for
ξ=17.5km/s (1)
169-172 I4 m/s pos20.0 Position of the cross-correlation peak for
ξ=20.0km/s (1)
--------------------------------------------------------------------------------
Note (1): ξ is the broadening parameter applied in the convolution of the
synthetic spectra. A negative value of the peak position corresponds
to a blueshift.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID Internal object identifier
4- 12 A9 --- Name Hiparcos number (HIP NNNNN)
14- 18 F5.2 pc r-rc Distance from the cluster center
20- 23 F4.2 pc e_r-rc Error on r-rc
25- 30 F6.3 km/s Valpha Tangential component in the α direction
for the astrometric vectors computed from
Gaia DR1 (Gaia Collaboration
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337) (1)
32- 36 F5.3 km/s e_Valpha Error on Valpha
38- 44 F7.3 km/s Vdelta Tangential component in the δ direction
for the astrometric vectors computed from
Gaia DR1 (Gaia Collaboration
2017A&A...601A..19G 2017A&A...601A..19G, Cat. I/337) (1)
46- 50 F5.3 km/s e_Vdelta Error on Vdelta
--------------------------------------------------------------------------------
Note (1): The tangential components are given by Valpha=kµα*/π
and Vdelta=kµδ/π, where
µα*=µαcosδ and µδ are the
proper motions given in mas/yr, π is the parallax given in mas,
and k=4.74047 km.yr/s is the factor that transforms from au/yr to km/s
--------------------------------------------------------------------------------
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(End) Ana Fiallos [CDS] 02-Aug-2022