a detailed study with both a full pulsation analysis and dedicated spectroscopy
| reference | Telting et al. 2014, A&A 570, A129 |
| title | KIC 7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf |
| Kepler data used | the near-continuous 2.88 yr light curve |
| pulsations | Rich g-mode spectrum with a few low-amplitude p-modes; the orbital light-travel delay of 27 s was measured by timing the pulsations |
| orbit | P = 14.2 d, K = 39 km/s from three independent routes (spectra, Doppler beaming at 163 ppm, pulsation timing); white dwarf minimum mass 0.40 Msun |
| spectra behind it | new ground-based low-resolution spectroscopy; high signal-to-noise AVERAGE spectra were used for the atmospheric parameters, giving nitrogen and iron abundances close to solar |
| atmospheric parameters | final adopted LTE values Teff 27700(300) K, log g 5.50(3), log(NHe/NH) -2.65(3); the NLTE fit gives 28100 / 5.55 |
| the spectrum behind it | The high signal-to-noise average spectra are here as the two -noOrbit means, NOT and WHT -- 23 NOT spectra and 6 WHT, shifted to rest before co-adding. J. Telting's January 2012 batch, which arrived in September 2026, holds an earlier pair of the same two observations made from 9 and 2 spectra without the orbit removed; they are in means/ and are not the published ones. |
| note | One of the strongest cases in the sample: three independent orbit determinations and a dedicated abundance analysis on averaged spectra. |
Paper: Telting14.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 |
|---|---|---|---|---|---|---|---|---|---|---|
| NOT | NOT / ALFOSC_FASU | 2011-06-01 | 23 | 355.2 | 1.98 | 27278 ± 37 | 5.578 ± 0.006 | -2.57 ± 0.02 | 0.90% | 3.47 |
| NOT-2008 | NOT / ALFOSC_FASU | 2008-09-21 | 1 | 106.9 | 4.82 | 27776 ± 238 | 5.602 ± 0.042 | -2.46 ± 0.08 | 1.80% | 1.21 |
| WHT ★ | WHT / ISIS blue arm | 2010-07-27 | 6 | 253.3 | 1.79 | 27565 ± 45 | 5.616 ± 0.008 | -2.53 ± 0.02 | 0.71% | 1.87 |
★ 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] | 1444 |
| parallax error [%] | 3.9 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.032 (0.020–0.042) |
| … the dust map | 0.0541 (SFD×disk(f=0.96)) |
| log Θ [rad] | -11.231 +0.006 −0.006 |
| R [R☉] | 0.188 +0.008 −0.007 |
| M [M☉] | 0.534 +0.081 −0.071 |
| L [L☉] | 18.4 +1.7 −1.5 |
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 27565 K and log g 5.616 from WHT, with 32 of the fitted bands and reduced χ² 0.08. 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, 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.
not/ and wht/ are the original 2013 fitprof22 working directories, kept as they were run, each with the line list of its own era. Neither holds an sp.spek, so fitk1 does not read them. The live directories are NOT/ and WHT/, extracted from the same two -noOrbit FITS and linked to the master. Both mean spectra were shifted to rest before co-adding -- 23 spectra for the NOT, 6 for the WHT -- because the star is an sdB+WD binary; the WHT was resampled onto the NOT's 0.765 A/px grid in the process, coarser than ISIS delivers. means/ holds an earlier pair of means of the same two observations, from toroy.tgz -- a bundle of 19 means of 9 Kepler-field stars reduced by J. Telting in January 2012 and sent in September 2026. They are the pre-orbit-solution versions: 9 NOT spectra and 2 WHT against the 23 and 6 of the -noOrbit means in use, and co-added without shifting to rest. The line profiles are nevertheless the same to a hundredth in depth and to better than 0.1 A in H-gamma width, so the orbit correction was never what mattered here -- the number of spectra was. Nothing is fitted from them; they are kept as the earlier state of the same data.