J/MNRAS/514/1071 RVs of GaiaDR2 comoving wide binary stars (Moschella+, 2022)
A measurement of stellar surface gravity hidden in radial velocity differences
of comoving stars.
Moschella M., Slone O., Dror J.A., Cantiello M., Perets H.B.
<Mon. Not. R. Astron. Soc. 514, 1071-1076 (2022)>
=2022MNRAS.514.1071M 2022MNRAS.514.1071M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, giant ; Stars, normal ;
Radial velocities ; Optical ; Photometry ; Positional data ;
Proper motions ; Parallaxes, trigonometric ;
Effective temperatures ; Abundances, [Fe/H] ; Stars, masses ;
Stars, diameters
Keywords: convection - gravitation - astrometry - (stars:) binaries: general
Abstract:
The gravitational redshift induced by stellar surface gravity is
notoriously difficult to measure for non-degenerate stars, since its
amplitude is small in comparison with the typical Doppler shift
induced by stellar radial velocity. In this study, we make use of the
large observational data set of the Gaia mission to achieve a
significant reduction of noise caused by these random stellar motions.
By measuring the differences in velocities between the components of
the pairs of comoving stars and wide binaries, we are able to
statistically measure the combined effects of gravitational redshift
and convective blueshifting of spectral lines, and nullify the effect
of the peculiar motions of the stars. For the subset of stars
considered in this study, we find a positive correlation between the
observed differences in Gaia radial velocities and the differences in
surface gravity and convective blueshift inferred from effective
temperature and luminosity measurements. The results rule out a null
signal at the 5σ level for our full data set. Additionally, we study
the subdominant effects of binary motion, and possible systematic
errors in radial velocity measurements within Gaia. Results from the
technique presented in this study are expected to improve
significantly with data from the next Gaia data release. Such
improvements could be used to constrain the mass-luminosity relation
and stellar models that predict the magnitude of convective blueshift.
Description:
The advent of the Gaia space telescope has given rise to a new era of
precision astrometry with a current catalogue that includes over one
billion stars, of which several millions have radial velocity (RV)
measurements. Such a large data set offers new opportunities to
statistically measure stellar properties. In this study, we use RV
measurements from Gaia to measure the gravitational redshift (GR) due
to stellar surface gravity (SG), as well as the subdominant effect of
convective outflows and downflows at the stellar surface.
Understanding these effects is important since they give rise to
systematic noise in RV measurements, and in particular raise
difficulties in RV detection of exoplanets. Additionally, measurement
of convective effects could shed light on the physical processes
occurring within stars and constrain current and future modelling of
these processes. In this study, we search for the GR in comoving pairs
of stars, thousands of which have been identified in Gaia DR2. If
these comoving pairs are wide binaries, their orbital velocities
should be small, providing a clean data set with which to study small
contributions to the RVs. In particular, the difference of the RVs of
two stars in a wide binary can be dominated by the difference in
vGR, especially for pairs of stars with sizeable differences in mass
and/or radius. This opens the possibility of using wide binaries to
directly probe GR and indirectly gain information regarding the
stellar structure and dynamics.
The main results of this study are presented in Fig. 1, which shows
the correlation between the differences of the observed RVs of stars
in comoving pairs and the expectation from the GR and CB effects. For
our data, we take stars are typically wide binaries with separation
distances ~> 25 au. In our cases we analyse the subset of SUPERWIDE
pairs that also have RV measurements in Gaia DR2. Additionally, we
require that the difference in the RVs of each star in a pair,
ΔRV has a small measurement error of SQRT( σRV,12
+σRV,22 ) < 1 km/s. Also we remove outlier pairs with
|ΔRV| > 5 km/s and require a tranverse separation above 10-3
pc. By taking only pairs which have complete Gaia DR2 astrometric
data, we can isolate MS and giants by selections as shown in the
figure 2 of the section 2. It provides 1135 pairs pass these
additional selection criteria in our primary data set, of which 1080
contain two MS stars, 53 contain one MS star and one giant, and two
contain two giant stars. In addition to the primary data sample, we
also identify a distinct set (i.e set of 114 pairs are marked in blue
in figure 2 of the section 2) of comoving pairs for which both stars
have high-quality spectroscopic mass and radius measurements from
Sanders & Das (2018MNRAS.481.4093S 2018MNRAS.481.4093S). We thus present these two data
sets in primary.dat and second.dat including estimated GR and CB
velocities of our analysis.
Objects:
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RA (ICRS) DE Designation(s)
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02 13 17.40 +36 10 42.3 Tri II = NAME Lae 2/Tri II
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
primary.dat 393 1135 Primary comoving star pairs sample
second.dat 393 114 Secondary comoving star pairs sample
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See also:
J/AJ/157/78 : Double & multiple star systems from GaiaDR2
(Jimenez-Esteban+, 2019)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/643/A146 : The solar gravitational redshift (Gonzalez Hernandez+, 2020)
J/A+A/550/A103 : Model 1D (LHD) and 3D (CO5BOLD) spectra
(Allende Prieto+, 2013)
J/A+A/526/A127 : Velocities of M67 main-sequence and giant stars
(Pasquini+, 2011)
J/ApJS/247/66 : SUPERWIDE: wide binaries in Gaia & SUPERBLINK
(Hartman+, 2020)
J/ApJS/236/42 : Asteroseismology of ∼16000 Kepler red giants (Yu+, 2018)
J/AJ/142/138 : All-sky catalog of bright M dwarfs (Lepine+, 2011)
J/AJ/135/2177 : High proper motion stars in the DSS. IV. (Lepine, 2008)
J/AJ/124/1190 : Northern high proper motion stars in DSS (Lepine+, 2002)
J/AJ/130/1247 : High proper motion stars in the DSS. III (Lepine+, 2005)
J/AJ/153/257 : Comoving stars in Gaia DR1 (Oh+, 2017)
J/MNRAS/382/1073 : M/L relation of intermediate-mass stars (Malkov+, 2007)
J/MNRAS/483/5026 : Radial velocities of Hyades stars (Leao+, 2019)
Byte-by-byte Description of file: primary.dat second.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2-1 Gaia DR2 unique source identifier of the
first comoving star (gaiasourceid1)
21- 39 I19 --- GaiaDR2-2 Gaia DR2 unique source identifier of the
second comoving star (gaiasourceid2)
41- 50 F10.7 mag G1mag G-band mean magnitude (Vega) of the first
comoving star from Gaia DR2 (G_mag1)
52- 61 F10.7 mag G2mag G-band mean magnitude (Vega) of the second
comoving star from Gaia DR2 (G_mag2)
63- 79 F17.14 mas Plx1 Absolute stellar parallax of the first
comoving star from Gaia DR2 (parallax1)
81- 97 F17.14 mas Plx2 Absolute stellar parallax of the second
comoving star from Gaia DR2 (parallax2)
99-119 F21.16 mas/yr pmRA1 Proper motion in right ascension direction
(pmRA*cosDE) of the first comoving star from
Gaia DR2 (pmra1)
121-141 F21.15 mas/yr pmRA2 Proper motion in right ascension direction
(pmRA*cosDE) of the second comoving star
from Gaia DR2 (pmra2)
143-154 F12.8 Lsun L1 Luminosity of the first comoving star from
Gaia DR2 (L1)
156-167 F12.9 Lsun L2 Luminosity of the second comoving star from
Gaia DR2 (L2)
169-177 F9.4 K T1 Effective temperature of the first comoving
star from Gaia DR2 (T1)
179-187 F9.4 K T2 Effective temperature of the second comoving
star from Gaia DR2 (T2)
189-209 F21.18 [Sun] [Fe/H]1 Iron to hydrogen abundance ratio of the
first comoving star from Gaia DR2 ([Fe/H]1)
211-230 F20.17 [Sun] [Fe/H]2 Iron to hydrogen abundance ratio of the
second comoving star from Gaia DR2 ([Fe/H]2)
232-248 F17.15 Msun M1 Estimated mass of the first comoving star
(m1) (1)
250-266 F17.15 Msun M2 Estimated mass of the second comoving star
(m2) (1)
268-285 F18.16 km/s vGR1 Gravitational redshift velocity of the first
comoving star defined as G*M1/R1 (gr1)
287-304 F18.16 km/s vGR2 Gravitational redshift velocity of the
second comoving star defined as G*M2/R2 (gr2)
306-327 A22 km/s vCB1 Convective blueshift velocity of the first
comoving star as defined in the section 4
(cb1)
329-350 A22 km/s vCB2 Convective blueshift velocity of the second
comoving star as defined in the section 4
(cb2)
352-371 F20.15 km/s RV1 Radial velocity of the first comoving star
from Gaia DR2 (rv1)
373-393 F21.16 km/s RV2 Radial velocity of the second comoving star
from Gaia DR2 (rv2)
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Note (1): For primary star sample, as explained in the section 2, we estimate
the masses from mass-luminosity relation equation 2 for MS stars and
determined mass from the Kepler mission for giant stars. For secondary
stars we use the mass and radius estimates provided in Sanders & Das
(2018MNRAS.481.4093S 2018MNRAS.481.4093S).
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 01-Apr-2025