J/ApJ/840/70 Historical and HST Astrometry of Sirius A,B (Bond+, 2017)
The Sirius system and its astrophysical puzzles:
Hubble Space Telescope and ground-based astrometry.
Bond H.E., Schaefer G.H., Gilliland R.L., Holberg J.B., Mason B.D.,
Lindenblad I.W., Seitz-McLeese M., Arnett W.D., Demarque P., Spada F.,
Young P.A., Barstow M.A., Burleigh M.R., Gudehus D.
<Astrophys. J. 840, 70 (2017)>
=2017ApJ...840...70B 2017ApJ...840...70B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Positional data
Keywords: astrometry - binaries: visual - stars: fundamental parameters -
stars: individual (Sirius) - stars: white dwarfs
Abstract:
Sirius, the seventh-nearest stellar system, is a visual binary
containing the metallic-line A1 V star Sirius A, the brightest star in
the sky, orbited in a 50.13 year period by Sirius B, the brightest and
nearest white dwarf (WD). Using images obtained over nearly two
decades with the Hubble Space Telescope (HST), along with photographic
observations covering almost 20 years and nearly 2300 historical
measurements dating back to the 19th century, we determine precise
orbital elements for the visual binary. Combined with the parallax and
the motion of the A component, these elements yield dynamical masses
of 2.063±0.023M☉ and 1.018±0.011M☉ for Sirius A and B,
respectively. Our precise HST astrometry rules out third bodies
orbiting either star in the system, down to masses of
∼15-25M{Jup}. The location of Sirius B in the Hertzsprung-Russell
diagram is in excellent agreement with theoretical cooling tracks for
WDs of its dynamical mass, and implies a cooling age of ∼126Myr. The
position of Sirius B on the mass-radius plane is also consistent
with WD theory, assuming a carbon-oxygen core. Including the pre-WD
evolutionary timescale of the assumed progenitor, the total age of
Sirius B is about 228±10Myr. We calculated evolutionary tracks for
stars with the dynamical mass of Sirius A, using two independent
codes. We find it necessary to assume a slightly subsolar metallicity,
of about 0.85Z☉, to fit its location on the luminosity-radius
plane. The age of Sirius A based on these models is about 237-247Myr,
with uncertainties of ±15Myr, consistent with that of the WD
companion. We discuss astrophysical puzzles presented by the Sirius
system, including the probability that the two stars must have
interacted in the past, even though there is no direct evidence for
this and the orbital eccentricity remains high.
Description:
We have assembled a compilation of published historical measurements
of the position angle (PA) and the angular separation of Sirius B
relative to Sirius A. Our tabulation is based on a critical review of
measures contained in the Washington Double Star Catalog maintained at
the USNO and from our additional literature searches. Notes included
in the tabulation give extensive commentary on the historical
observations.
Many early publications provided measures averaged over multiple
nights or even an entire observing season for the purpose of reducing
computational labor in subsequent analyses. With modern computers,
there is no need for such averaging, so we opted to present the
individual measures whenever available. However, if an observer
reported more than one measurement on a given night, we did compute
the mean position for that night. If the original publication only
reported a mean across several nights, we tabulated that mean as
reported.
The visual micrometer observations did not always include a
contemporaneous measurement of both the PA and separation. These
omissions are listed as -99.0 in the table. The measurement
uncertainties were assigned through our orbital fitting method
described in the paper. Measurements that were rejected from the
orbital solution are identified in the Notes column and are listed
with uncertainties of 0.
Objects:
----------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------
06 45 08.92 -16 42 58.0 Sirius = * alf CMa
----------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
sirius.dat 157 2367 Astrometry of Sirius B relative to A
notes.dat 79 151 Additional notes
refs.dat 187 366 References
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See also:
J/A+A/299/621 : Is Sirius a triple star? (Benest+, 1995)
J/A+AS/136/293 : Sirius photographic observations (Jasinta+, 1999)
J/ApJS/126/461 : Equivalent Widths in the Spectrum of Sirius (Zhao+, 2000)
J/AJ/146/68 : Spectra of Vega, Sirius, GD153, and HD209458 (Linnell+, 2013)
Byte-by-byte Description of file: sirius.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "date" Date Observation date; YYYY-MMM-DD (1)
13- 21 F9.4 yr Year Besselian Year
24- 30 F7.3 deg PAmeas ?=-99.0 Measured position angle
33- 40 F8.4 arcsec Sepmeas ?=-99.0 Measured separation
44- 50 F7.3 deg PAcor ?=-99.0 Corrected position angle (2)
53- 57 F5.3 deg e_PAcor Adopted uncertainty in PAcor (3)
59- 66 F8.4 arcsec Sepcor ?=-99.0 Corrected separation (2)
69- 74 F6.4 arcsec e_Sepcor Adopted uncertainty in SepCor (3)
77- 98 A22 --- ObsCode Observer name and reference code (4)
101 A1 --- Method Method Code (5)
103-105 F3.1 m Tel Size of telescope aperture
107-114 A8 --- Notes Code for additional notes (6)
116-134 A19 --- Bibcode ? Bibcode for the primary reference
137-157 A21 --- Ref ? Additional reference codes
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Note (1): Observation date if the decimal year is not given in the original
publication. If this is the case, then the Besselian year is computed from
that date. Otherwise the decimal year is used directly from the publication.
Note (2): Corrected for precession and space motion.
Note (3): 0 for measurements that were rejected from the orbital solution.
Note (4): Last name of observer and year of publication.
The full references are detailed in the file refs.dat.
Note (5): Method Code as follows:
M = Micrometer
P = Photographic
C = CCD
H = Hubble Space Telescope
Note (6): Individually numbered notes are detailed below with the coding of
R: Rejections
C: Corrections
M: Mean measurements
N: general Notes on measurements
U: Unresolved observations
and detailled in notes.dat file.
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Byte-by-byte Description of file: notes.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- Notes Note code
5- 79 A75 --- Text Text of the note
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Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 22 A22 --- ObsCode Observer and reference code from sirius.dat
24- 42 A19 --- Bibcode Bibcode for the reference
45-187 A143 --- Text Full reference text (1)
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Note (1): The observer is listed in parentheses if the observer is different
from the corresponding author of the publication.
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Acknowledgements:
Gail H. Schaefer, schaefer(at)chara-array.org
(End) Gail H. Schaefer [Georgia State Univ.], Patricia Vannier [CDS] 19-May-2017