The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system
S. Fauvaud
(1, 2)
,
Jean-Pierre Sareyan
(3, 4)
,
Ignasi Ribas
(5)
,
E. Rodríguez
(6)
,
P. Lampens
(7)
,
G. Klingenberg
(8)
,
J. A. Farrell
(9)
,
F. Fumagalli
(2)
,
J. H. Simonetti
(10)
,
M. Wolf
(11)
,
G. Santacana
(1)
,
A.-Y. Zhou
(12)
,
R. Michel
(13)
,
L. Fox Machado
(13)
,
M. Alvarez
(13)
,
A. Nava-Vega
(14)
,
M. J. López-González
(6)
,
V. M. Casanova
(6)
,
F. J. Aceituno
(6)
,
I. Scheggia
(15)
,
J.-J. Rives
(16)
,
E. G. Hintz
(17)
,
P. van Cauteren
(18)
,
M. Helvaci
(19)
,
C. Yesilyaprak
(20)
,
K. A. Graham
(21)
,
L. Král
(22)
,
R. Kocián
(22)
,
H. Kucáková
(22)
,
M. Fauvaud
(1)
,
B. H. Granslo
(8)
,
J. Michelet
(23)
,
M. P. Nicholson
(21)
,
J.-M. Vugnon
(24)
,
L. Kotková
(25)
,
K. Truparová
(22)
,
C. Ulusoy
(26)
,
B. Yasarsoy
(26)
,
A. Avdibegovic
(11)
,
M. Blaiek
(11)
,
J. Kliner
(11)
,
P. Zasche
(11)
,
S. Bartosíková
(22)
,
M. Vilásek
(22)
,
O. Trondal
(8)
,
F. van den Abbeel
(27)
,
Raoul Behrend
(28)
,
H. Wücher
(1)
1
Observatoire du Bois de Bardon
2 GEOS - Groupe européen d’observation stellaire
3 Observatoire de la Côte d'Azur
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 ICE - Institut de Ciencies de l'Espai
6 IAA - Instituto de Astrofísica de Andalucía
7 Koninklijke Sterrenwacht van België
8 Variable Star Section, Norwegian Astronomical Society
9 Sulphur Flats Observatory
10 Martin Observatory, Physics Dep., Virginia Polytechnic Institute & State University, Blacksburg
11 UK - Univerzita Karlova [Praha, Česká republika] = Charles University [Prague, Czech Republic]
12 National Astronomical Observatoires-CAS
13 Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México
14 Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California
15 Societá Astronomica Le pleiadi
16 Observatoire des Trois Korrigans
17 Department of Physics and Astronomy, Brigham Young University
18 Beersel Hills Observatory
19 Akdeniz University
20 Atatürk Üniversitesi = Ataturk University
21 AAVSO - American Association of Variable Star Observers
22 Project Eridanus, Observatory and Planetarium of Johann Palisa
23 CALA - Club d'Astronomie Lyon Ampéré [Vaulx-en-Velin]
24 Club Eclipse : Club d'Etudes du Ciel, de la Lune, des Instruments, des Planètes, du Soleil et des Etoiles...
25 Astronomical Institute, Academy of Sciences
26 Ege University Observatory
27 Vesqueville Observatory
28 ObsGE - Observatoire Astronomique de l'Université de Genève
2 GEOS - Groupe européen d’observation stellaire
3 Observatoire de la Côte d'Azur
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 ICE - Institut de Ciencies de l'Espai
6 IAA - Instituto de Astrofísica de Andalucía
7 Koninklijke Sterrenwacht van België
8 Variable Star Section, Norwegian Astronomical Society
9 Sulphur Flats Observatory
10 Martin Observatory, Physics Dep., Virginia Polytechnic Institute & State University, Blacksburg
11 UK - Univerzita Karlova [Praha, Česká republika] = Charles University [Prague, Czech Republic]
12 National Astronomical Observatoires-CAS
13 Observatorio Astronómico Nacional, Instituto de Astronomía, Universidad Nacional Autónoma de México
14 Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California
15 Societá Astronomica Le pleiadi
16 Observatoire des Trois Korrigans
17 Department of Physics and Astronomy, Brigham Young University
18 Beersel Hills Observatory
19 Akdeniz University
20 Atatürk Üniversitesi = Ataturk University
21 AAVSO - American Association of Variable Star Observers
22 Project Eridanus, Observatory and Planetarium of Johann Palisa
23 CALA - Club d'Astronomie Lyon Ampéré [Vaulx-en-Velin]
24 Club Eclipse : Club d'Etudes du Ciel, de la Lune, des Instruments, des Planètes, du Soleil et des Etoiles...
25 Astronomical Institute, Academy of Sciences
26 Ege University Observatory
27 Vesqueville Observatory
28 ObsGE - Observatoire Astronomique de l'Université de Genève
Résumé
Context. Short-period high-amplitude pulsating stars of Population I (delta Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given.
Aims: We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses.
Methods: An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months.
Results: In addition to a positive (161 ± 3) × 10-9 yr-1 secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short- (144.2 d) and long-term (~3400 d) variations, both incompatible with a scenario of stellar evolution.
Conclusions: Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M_&sun;) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star (>=0.03 M_&sun;), orbiting in ~3400 d at a distance of 4.5 AU from the primary.
Aims: We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses.
Methods: An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months.
Results: In addition to a positive (161 ± 3) × 10-9 yr-1 secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short- (144.2 d) and long-term (~3400 d) variations, both incompatible with a scenario of stellar evolution.
Conclusions: Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M_&sun;) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star (>=0.03 M_&sun;), orbiting in ~3400 d at a distance of 4.5 AU from the primary.