a detailed study with both a full pulsation analysis and dedicated spectroscopy
| reference | Silvotti et al. 2012, MNRAS 424, 1752 |
| title | Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf |
| Kepler data used | 605 days |
| pulsations | Not a pulsator. Ellipsoidal deformation at twice the orbital frequency and Doppler beaming at 432 +- 5 ppm |
| orbit | P = 0.15749747(25) d (3.779939 h); photometric K1 = 85.8 km/s against a spectroscopic 97.2 +- 2.0 km/s; maximum inclination ~40 deg, most likely i ~ 20 deg |
| the spectrum behind it | The atmospheric parameters come from WHT spectroscopy, which is here. The 22 KPNO 4m spectra used for the radial velocities are not, but they do not bear on the parameters. |
| note | An unusually low-mass sdB. The 2012 fitting directory here (int/) used its third axis for METALLICITY, not helium -- p00.grid and m10.grid are [M/H] = 0.0 and -1.0 -- so the "nHe" in that fit.out is Z. |
Paper: Silvotti12.pdf, in /home/roy/sync/old/sddoc.
| observation | telescope | date | n | S/N | FWHM [Å] | Teff [K] | log g | log n(He)/n(H) | residual | χ² |
|---|---|---|---|---|---|---|---|---|---|---|
| INT ★ | INT / IDS | 2010-06-27 | 10 | 219.7 | 3.00 | 23281 ± 118 | 5.779 ± 0.014 | -3.55 | 1.00% | 1.53 |
| WHT | WHT / ISIS blue arm | 2009-04-13 | 1 | 74.5 | 5.00 | 22763 ± 254 | 5.596 ± 0.034 | -3.55 | 2.12% | 1.59 |
★ marks the observation adopted for the sample table — the one with the smallest residual, which is what says how well the model reproduces the spectrum. Signal-to-noise does not.
The line fit gives a temperature and a gravity but says nothing about size. Held at those parameters, the broadband spectral energy distribution has one free scale — the angular diameter — and the Gaia parallax turns that into a radius. Then M = gR²/G, which is linear in g: a tenth of a dex in gravity is 26 per cent in mass, so this is where the gravity scale bites hardest.
| distance [pc] | 1254 |
| parallax error [%] | 4.0 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.070 (0.056–0.084) |
| … the dust map | 0.0962 (SFD×disk(f=0.83)) |
| log Θ [rad] | -11.286 +0.008 −0.007 |
| R [R☉] | 0.144 +0.007 −0.006 |
| M [M☉] | 0.456 +0.071 −0.061 |
| L [L☉] | 5.5 +0.6 −0.5 |
Bamberg v25 ATLAS12 through the real filter curves, reddened by Fitzpatrick (1999) — its A(5500)/E(B−V) is 3.03, so this E(B−V) and the E(44−55) of Heber's group are the same number to under one per cent. Prescribed at 23281 K and log g 5.779 from INT, with 33 of the fitted bands and reduced χ² 0.16. The gravity error carried into the mass is 0.050 dex — the scatter between telescopes, not the formal error, because the formal one would claim a two per cent mass.
Bands left out: Johnson:B, GALEX:NUV, GALEX:FUV, 2MASS:H, 2MASS:J, 2MASS:Ks, WISE:W3, WISE:W4, GAIA/GAIA3:G, GAIA/GAIA3:Gbp, GAIA/GAIA3:Grp, SDSS:u, SDSS:g, SDSS:r, SDSS:i, SDSS:z, SDSS:u/SDSS:u', SDSS:g/SDSS:g', SDSS:r/SDSS:r', SDSS:i/SDSS:i', SDSS:z/SDSS:z', Johnson:U, Johnson:V, Cousins:U.
int/ and wht/ are copies of the 2012 fitprof22 working directories from data/spek/kepler (K06614501 and KepVI/sdB/J19368+4201), kept as they were run. Neither holds an sp.spek, so fitk1 does not read them. The live directories are INT/ and WHT/, linked to the master. Two things about the old work. Its third fitted axis was METALLICITY, not helium: runfit20.dat lists p00.grid and m10.grid, the [M/H] = 0.0 and -1.0 members of the h999 (helium-poor) family, so the "nHe = -1.4377" in int/fit.out is Z, not an abundance. The newA/newAm10/newAm20/newAp00 directories are the same experiment at fixed [M/H]. It also used vsini = 50 km/s, which the Python fitter cannot do. INT/ is taken from comb.spek rather than comb.fits: the FITS array runs down to 1348 A, far below the atmospheric cutoff, and comb.spek is the trimmed 3000-6940 A extraction.