J/ApJ/926/17 25yr observations of the sdB star AQ Col (Otani+, 2022)
Anomalous orbital characteristics of the AQ Col (EC 05217-3914) system.
Otani T., Lynas-Gray A.E., Kilkenny D., Koen C., von Hippel T.,
Uzundag M., Vuckovic M., Pennock C.M., Silvotti R.
<Astrophys. J., 926, 17 (2022)>
=2022ApJ...926...17O 2022ApJ...926...17O
ADC_Keywords: Stars, subdwarf; Photometry; Optical; Stars, double and multiple
Keywords: Multiple stars ; Variable stars ; Subdwarf stars ;
Extreme horizontal branch stars ; Stellar evolution ;
Timing variation methods ; Pulsation frequency method ;
White dwarf stars
Abstract:
AQ Col (EC 05217-3914) is one of the first detected pulsating subdwarf
B (sdB) stars and has been considered to be a single star. Photometric
monitoring of AQ Col reveals a pulsation timing variation with a
period of 486 days, interpreted as time delay due to reflex motion in
a wide binary formed with an unseen companion with expected mass
larger than 1.05M☉. The optical spectra and color-magnitude
diagram of the system suggested that the companion is not a
main-sequence star but a white dwarf or neutron star. The pulsation
timing variation also shows that the system has an eccentricity of
0.424, which is much larger than any known sdB long period binary
system. That might be due to the existence of another short period
companion to the sdB star. Two optical spectra obtained on
1996-December-5 show a radial velocity change of 49.1km/s in 46.1min,
which suggests the hot subdwarf in the wide binary is itself a close
binary formed with another unseen white dwarf or neutron star
companion; if further observations show this interpretation to be
correct, AQ Col is an interesting triple system worthy of further
study.
Description:
So far, we have photometric data spread over nearly 25yr for AQ Col.
In this paper, we present the results of our pulsation timing
analysis, and the extracted orbital information for the system. The
observation log (spanning 1996-Jan-28 to 2020-Mar-21) is presented in
Table 1. For observations made at the Southeastern Association for
Research in Astronomy at Cerro Tololo Inter-American Observatory,
Chile (SARA-CT), no filter has been used.
The early data in Table 1 were obtained using a mixture of the SAAO 1m
telescope with a photomultiplier-based photometer, or the SAAO 0.75m
and 1m telescopes with the UCT CCD photometer. All later observations
were made with the SAAO 1m telescope with different charge-coupled
device (CCD) photometers. See Section 2.1.
Objects:
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RA (ICRS) DE Designation(s)
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05 23 25.47 -39 11 54.0 AQ Col = EC 05217-3914
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 33 42 *Observation log for AQ Col
table4.dat 47 42 Pulsation timing variation data for F1 (4.67mHz),
F2 (4.63mHz), and F3 (4.60mHz) pulsation modes
after removing the quadratic fits
fig1.dat 25 28498 Light curve for AQ Col
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Note on table1.dat: Only the observation dates in which the data show any
pulsation amplitude ≥2σ above the noise level are shown. The
1996 and 1998 data were previously published in Koen+ (1999MNRAS.306..213K 1999MNRAS.306..213K).
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See also:
VI/39 : Model Atmospheres (Kurucz, 1979)
VI/65 : Evolutionary models of evolved stars (Dorman+ 1993)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
J/ApJ/419/596 : Pop I UV radiation models (Dorman+, 1993)
J/MNRAS/287/867 : Edinburgh-Cape Blue Object Survey. Zone 1. (Kilkenny+ 1997)
J/A+A/513/A6 : NOT survey of subdwarf B stars (Ostensen+, 2010)
J/MNRAS/421/2798 : Radial velocity monitoring of PG 1018-047 (Deca+, 2012)
J/MNRAS/431/240 : Edinburgh-Cape Blue Object Survey. III. (O'Donoghue+, 2013)
J/A+A/576/A44 : Hot subdwarf binaries from MUCHFUSS (Kupfer+, 2015)
J/MNRAS/459/4343 : Edinburgh-Cape Blue Object Survey. (Kilkenny+, 2016)
J/MNRAS/466/1290 : Metal-rich SX Phe stars in Kepler field (Nemec+, 2017)
J/A+A/610/A17 : RV of candidate hybrid variable stars (Lampens+, 2018)
J/MNRAS/474/4322 : Orbital parameters of 341 new binaries (Murphy+, 2018)
J/ApJ/859/145 : 20yr observations of EC 20117-4014 (Otani+, 2018)
J/A+A/611/A48 : Seven sdB eclipsing binaries data (Pulley+, 2018)
J/A+A/611/A85 : Time-series photometry of V391 Peg (Silvotti+, 2018)
J/A+A/621/A38 : Gaia catalogue of hot subluminous stars (Geier+, 2019)
J/A+A/638/A108 : 4 p-mode pulsators arrival times (Mackebrandt+, 2020)
J/A+A/649/A3 : Gaia EDR3 photometric passbands (Riello+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 "Y/M/D" Date Date of observation (UT)
13- 20 F8.2 d BJD [-3388.6/5430.28] Mean observation time;
BJD-2453500
22- 26 F5.1 min Dur [86.8/460.4] Observation length
28- 33 A6 --- Obs Observatory (1)
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Note (1): Observatory as follows:
SAAO = South African Astronomical Observatory (31 occurrences)
SARA-S = Southeastern Association for Research in Astronomy at
Cerro Tololo Inter-American Observatory (11 occurrences)
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 11 F11.2 d BJD [-3368.71/5430.28] Mid observation time;
BJD-2454000
13- 18 F6.1 s O-CF1 [-252.5/333.7]? F1 pulsation timing variations
20- 23 F4.1 s e_O-CF1 [1.7/41.1]? Uncertainty in O-C(F1)
25- 30 F6.1 s O-CF2 [-256.3/299.3]? F2 pulsation timing variations
32- 35 F4.1 s e_O-CF2 [4.2/29.7]? Uncertainty in O-C(F2)
37- 42 F6.1 s O-CF3 [-248.8/303.8]? F3 pulsation timing variations
44- 47 F4.1 s e_O-CF3 [4.1/31.5]? Uncertainty in O-C(F3)
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Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date
16- 25 F10.7 mag mag [-0.2/0.21] Observed magnitude
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 15-Sep-2023