2016A&A...589A...1R


Query : 2016A&A...589A...1R

2016A&A...589A...1R - Astronomy and Astrophysics, volume 589A, 1-1 (2016/5-1)

Pulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch.

RANDALL S.K., CALAMIDA A., FONTAINE G., MONELLI M., BONO G., ALONSO M.L., VAN GROOTEL V., BRASSARD P., CHAYER P., CATELAN M., LITTLEFAIR S., DHILLON V.S. and MARSH T.R.

Abstract (from CDS):

We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 h of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, Teff and log N(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48 000 and 54 000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ∼2700s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in logg-Teff space. This can be directly compared to the pulsation driving predicted from the Montreal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29 000-36000K where the rapid subdwarf B pulsators are found is complemented by a second one above 50000K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample.

Abstract Copyright: © ESO, 2016

Journal keyword(s): stars: oscillations - stars: horizontal-branch - subdwarfs - globular clusters: individual: ω Centauri - stars: variables: general

VizieR on-line data: <Available at CDS (J/A+A/589/A1): table5.dat spfc/* sps/*>

Nomenclature: Table 5: [RCF2016] NNNNNNN N=45 among (Nos 53945-5262593). Table 5: [RCF2011] VN (No V5) added = Cl* NGC 5139 SAW VNNN (No V460) added.

Simbad objects: 57

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Number of rows : 57
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1296 0
2 Cl* NGC 5139 BPB 177506 HB* 13 26 00.7 -47 29 28 17.513 18.724 18.855 18.906 19.130 ~ 5 0
3 [MDL2011] 64729 HB* 13 26 08.520 -47 29 41.69 17.381 18.825 18.952 18.952 18.995 ~ 4 0
4 [MDL2011] 70950 HB* 13 26 12.620 -47 28 31.94 16.921 18.427 18.551 18.551 18.497 ~ 4 0
5 [RCF2016] 5262593 HB* 13 26 12.620 -47 27 22.38 16.546 17.810 17.938 17.938 18.028 ~ 4 0
6 [MDL2011] 74057 HB* 13 26 14.640 -47 28 32.32 17.215 18.657 18.824 18.824 19.032 ~ 4 0
7 Cl* NGC 5139 SAW V454 HB* 13 26 15.00 -47 33 05.8 16.721 18.205 18.42 18.415 18.57 ~ 6 0
8 [RCF2016] 5205350 HB* 13 26 15.370 -47 30 41.11 17.012 18.462 18.616 18.616 18.804 ~ 4 0
9 [RCF2016] 5220684 HB* 13 26 15.400 -47 26 24.39 17.093 18.500 18.748 18.727 19.045 ~ 4 0
10 [MDL2011] 75981 HB* 13 26 15.9 -47 28 09 16.899 18.313 18.513 18.513 18.692 ~ 4 0
11 [MDL2011] 75993 HB* 13 26 15.9 -47 28 30 16.847 18.206 18.359 18.359 18.444 ~ 5 0
12 [RCF2016] 5138707 HB* 13 26 17.940 -47 30 32.89 17.806 19.094 19.407 19.293 19.992 ~ 4 0
13 [RCF2016] 165237 HB* 13 26 19.570 -47 31 13.67 16.889 18.335 18.535 18.546 18.744 ~ 4 0
14 [RCF2016] 165943 HB* 13 26 19.880 -47 30 15.84 17.349 18.513 18.916 18.764 19.040 ~ 4 0
15 [RCF2016] 168035 HB* 13 26 20.760 -47 32 28.65 16.593 17.929 18.098 18.084 18.263 ~ 4 0
16 [RCF2016] 5238307 HB* 13 26 22.210 -47 30 52.70 17.734 18.590 18.606 18.673 18.583 ~ 4 0
17 [RCF2016] 172409 HB* 13 26 22.640 -47 28 03.13   18.151   18.456   ~ 1 0
18 [RCF2016] 5180753 HB* 13 26 22.920 -47 28 29.77 17.012 18.400 18.746 18.599 18.942 ~ 4 0
19 [RCF2016] 175411 HB* 13 26 23.970 -47 26 46.57   18.698   18.713   ~ 1 0
20 Cl* NGC 5139 SAW V453 HB* 13 26 24.74 -47 24 51.8 16.825 18.300 18.54 18.583 18.74 ~ 7 0
21 [RCF2016] 177614 HB* 13 26 24.920 -47 25 28.98 16.928 18.443 18.615 18.699 18.610 ~ 4 0
22 [RCF2016] 177711 HB* 13 26 24.930 -47 25 46.28 17.299 18.591 18.351 18.796 18.049 ~ 4 0
23 [RCF2016] 204071 HB* 13 26 37.220 -47 29 55.79 16.861 17.929 18.173 18.100 18.281 ~ 4 0
24 [RCF2016] 5142638 HB* 13 26 45.640 -47 34 02.37 17.342 18.811 18.919 18.919 19.001 ~ 4 0
25 NGC 5139 GlC 13 26 47.28 -47 28 46.1   6.12 5.33     ~ 3120 0
26 [RCF2016] 5102280 HB* 13 26 49.020 -47 35 47.95 16.856 18.357 18.441 18.441 18.432 ~ 4 0
27 [RCF2016] 5164025 HB* 13 26 53.670 -47 33 11.99 17.466 18.878 19.037 19.037 19.241 ~ 4 0
28 [RCF2016] 5059328 HB* 13 26 55.500 -47 30 06.07   18.874   19.075   ~ 1 0
29 [MDL2011] 135227 HB* 13 26 56.2 -47 34 37   18.816   18.985   ~ 2 0
30 [RCF2016] 5085696 HB* 13 26 56.8294885133 -47 36 43.000829163 17.316 18.747 18.744 18.744 18.603 ~ 4 0
31 [RCF2016] 5143191 HB* 13 26 59.170 -47 30 19.17   18.137   18.339   ~ 1 0
32 [RCF2016] 248955 HB* 13 26 59.170 -47 30 26.75   18.014   18.192   ~ 1 0
33 [RCF2016] 5141232 HB* 13 27 02.990 -47 34 05.36 17.134 18.578 18.739 18.739 18.968 ~ 4 0
34 [RCF2016] 5039935 HB* 13 27 03.110 -47 31 53.49 16.134 19.160 19.477 19.314 20.046 ~ 4 0
35 Cl* NGC 5139 SAW V452 HB* 13 27 04.84 -47 32 32.3   18.438 18.42 18.638 18.21 ~ 3 0
36 [RCF2016] 264057 HB* 13 27 06.470 -47 30 50.92 17.280 18.583 18.871 18.777 19.239 ~ 4 0
37 [RCF2016] 5062474 HB* 13 27 06.560 -47 29 46.54 17.672 18.919 18.385 18.938 17.886 ~ 4 0
38 [RCF2016] 5170422 HB* 13 27 07.880 -47 32 53.13 16.922 18.352 18.454 18.454 18.408 ~ 4 0
39 Cl* NGC 5139 BPB 152744 HB* 13 27 09.450 -47 30 41.18 17.325 18.692 18.277 18.892   ~ 2 0
40 [RCF2016] 5139614 HB* 13 27 09.810 -47 30 29.88 17.613 18.823 19.039 18.934 19.207 ~ 4 0
41 [RCF2016] 5119720 HB* 13 27 09.960 -47 31 34.89 17.203 18.619 18.856 18.778 19.095 ~ 4 0
42 [RCF2016] 5165122 HB* 13 27 10.310 -47 33 08.87 17.160 18.601 18.775 18.775 19.000 ~ 4 0
43 [RCF2016] 274052 HB* 13 27 11.460 -47 30 13.74 17.301 18.720 18.823 18.883 18.767 ~ 4 0
44 Cl* NGC 5139 SAW V451 HB* 13 27 11.77 -47 32 29.0 16.813 18.299 18.46 18.547 18.52 ~ 6 0
45 Cl* NGC 5139 BPB 149467 HB* 13 27 14.9630 -47 30 50.853 17.176 18.506 18.680 18.719 18.230 ~ 6 0
46 [MDL2011] 164808 HB* 13 27 16.1 -47 34 02 17.217 18.549 18.735 18.735 19.008 ~ 5 0
47 [RCF2016] 5124244 HB* 13 27 17.090 -47 34 46.20 17.250 18.892 19.033 19.033 19.193 ~ 4 0
48 [RCF2016] 5047695 HB* 13 27 17.360 -47 31 11.18 17.514 18.968 19.075 19.122 18.358 ~ 4 0
49 [RCF2016] 5185548 HB* 13 27 19.640 -47 31 55.85   18.116   18.251   ~ 1 0
50 V* V361 Hya ** 14 05 33.00 -27 01 34.1   15.45 15.26 15.16   sdB+ 110 0
51 CD-30 11223 HS* 14 11 16.1539612427 -30 53 03.692295694   11.90 11.90     sdB+DA 48 0
52 V* V499 Ser HS* 16 00 43.6054215157 +07 48 02.879107935           sdOHe 26 0
53 PG 1621+476 HS* 16 22 56.6649994821 +47 30 51.124980311   16.07 16.19     sdB+dM 34 0
54 PG 1716+426 HS* 17 18 03.8584285848 +42 34 12.566188858   13.69 13.97     sdB2VIIHe3 99 0
55 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1856 0
56 KPD 1930+2752 HS* 19 32 14.8086352823 +27 58 35.444970697 12.80 13.75 13.82     sdB 146 0
57 LS IV -14 116 HS* 20 57 38.8745387224 -14 25 43.995275738 11.63 12.73 13.02 13.28   sdB0.5VIIHe18 64 0

    Equat.    Gal    SGal    Ecl

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2021.07.29-08:58:20

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