J/MNRAS/421/2798 Radial velocity monitoring of PG 1018-047 (Deca+, 2012)
PG 1018-047: the longest period subdwarf B binary.
Deca J., Marsh T.R., Ostensen R.H., Morales-Rueda L., Copperwheat C.M.,
Wade R.A., Stark M.A., Maxted P.F.L., Nelemans G., Heber U.
<Mon. Not. R. Astron. Soc., 421, 2798-2808 (2012)>
=2012MNRAS.421.2798D 2012MNRAS.421.2798D
ADC_Keywords: Binaries, spectroscopic ; Stars, subdwarf ; Radial velocities
Keywords: binaries: close - binaries: spectroscopic - stars: evolution -
stars: individual: PG 1018-047 - subdwarfs
Abstract:
About 50 per cent of all known hot subdwarf B stars (sdBs) reside in
close (short-period) binaries, for which common-envelope ejection is
the most likely formation mechanism. However, Han et al.
(2002MNRAS.336..449H 2002MNRAS.336..449H, 2003MNRAS.341..669H 2003MNRAS.341..669H) predict that the majority
of sdBs should form through stable mass transfer leading to
long-period binaries. Determining orbital periods for these systems is
challenging and while the orbital periods of ∼100 short-period systems
have been measured, there are no periods measured above 30d. As part
of a large programme to characterize the orbital periods of sdB
binaries and their formation history, we have found that PG 1018-047
has an orbital period of 759.8±5.8d, easily making it the longest
period ever detected for a sdB binary. Exploiting the Balmer lines of
the subdwarf primary and the narrow absorption lines of the companion
present in the spectra, we derive the radial velocity amplitudes of
both stars, and estimate the mass ratio MMS/MsdB=1.6±0.2. From
the combination of visual and infrared photometry, the spectral type
of the companion star is determined to be mid-K.
Description:
We have observed PG 1018-047 spectroscopically with several different
instrument setups over a period of 10yr. The data were obtained using
the Isaac Newton Telescope (INT), William Herschel Telescope (WHT)
and Nordic Optical Telescope (NOT) on the island of La Palma, the
Radcliffe telescope at the South African Astronomical Observatory
(SAAO) and the Hobby-Eberly Telescope (HET) located at the McDonald
Observatory in Texas.
Objects:
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RA (2000) DE Designation(s)
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10 21 10.59 -04 56 19.6 PG 1018-047 = 2MASS J10211058-0456195
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 55 22 Journal of observations
table3.dat 22 125 The 125 RV measurements for PG 1018-047 with
their formal errors from the least-squares
fitting routine
tablea1.dat 30 119 RV measurements for PG 1018-047 with error and
offset correction, as used for the final
orbital fit results
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Date Observation date(s)
19- 23 A5 --- Setup Setup
25- 35 A11 --- Region lambda region
37- 38 I2 --- Nsp Number of spectra
40- 43 F4.2 0.1nm/pix Disp Mean dispersion (Å/pix)
45- 55 A11 --- Obs Observer(s) (1)
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Note (1): Observers' codes:
PFLM = P.F.L. Maxted
TA = T. Augustijn
TRM = T.R. Marsh
LM = Luisa Morales-Rueda
GN = G. Nelemans
CC = C. Copperwheat
RAW = R.A. Wade
MAS = M.A. Stark
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 d HJD Heliocentric Julian date (HJD-2450000)
11 A1 --- f_RV [abcd] Note on the data points (1)
13- 17 F5.1 km/s RV Radial velocity
19- 22 F4.1 km/s e_RV rms uncertainty on RV
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Note (1): Notes as follows:
a = The SAAO science frames belonging to these four RVs were made with very
marginal observing conditions. The resulting unreliable RVs are
therefore not considered in the remaining analysis.
b = This is a discrepant WHT data point, taken during service observations
in 2006. It is not in line with the other data taken on the same night
and therefore given no weight in the remaining analysis.
c = For the blue WHT science frames belonging to these two RVs, only a
single arc frame was available, taken before the first of the two
subsequent observations.
d = These two WHT observations in the Hbeta-Hdelta region had no flat-fields
or bias frames available.
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Setup Setup (1)
7- 17 F11.6 d HJD Heliocentric Julian date (HJD-2450000)
20- 24 F5.2 km/s RV Radial velocity
26- 30 F5.2 km/s e_RV rms uncertainty on RV
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Note (1): Setup informations:
INT-B : sigma=2.15km/s, offset=+0.85km/s
WHT-B : sigma=3.40km/s, offset=-2.01km/s
INT-R : sigma=2.15km/s, offset=+0.85km/s
WHT-R : sigma=3.40km/s, offset=-2.01km/s
SAAO : sigma=0km/s, offset=+4.63km/s
NOT : sigma=0km/s, offset= 0km/s
HET : sigma=0km/s, offset= 0km/s
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Mar-2013