a detailed study with both a full pulsation analysis and dedicated spectroscopy
| reference | Foster et al. 2015, ApJ 805, 94 |
| title | A pulsation analysis of Kepler observations of the subdwarf B star KIC 3527751 |
| Kepler data used | 3 yr of nearly continuous short cadence |
| pulsations | 251 periodicities, a hybrid pulsator; 189 (75%) associated with modes, including three l = 4 multiplets and possibly l = 9; l = 1 and 2 spacings 266.4 +- 0.2 and 153.2 +- 0.2 s; evidence of trapped modes |
| spectra behind it | KPNO 4m with RC-Spec/F3KB and the kpc-22b grating, 1.5-2.0 arcsec slit; NOT/ALFOSC grism #16; WHT/ISIS R600B with 0.8-1.0 arcsec slit. Exposures 600 s at KP4m and WHT, 300-500 s at NOT |
| atmospheric parameters | Teff 27818 +- 163 K, log g 5.35 +- 0.03, log N(He)/N(H) -2.99 +- 0.04, combined across observatories with systematics folded into the errors |
| the spectrum behind it | Foster et al. used KPNO 4m, NOT/ALFOSC grism #16 and WHT/ISIS R600B -- exactly the three spectra held here. J. Telting's January 2012 batch, which arrived in September 2026, holds the same three observations untrimmed; they are in means/ and confirm the identification, but the copies in data/ are what is fitted. |
| survey archive | A LAMOST DR11 spectrum exists and is here as LAMOST/, fitted in the LAMOST sample: 27560 +- 173 / 5.465 +- 0.026, agreeing with the WHT fit here to 4 K and 0.010 dex. |
| note | The three spectra this project holds for Samwise are exactly the three the paper used. |
Paper: Foster15.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 |
|---|---|---|---|---|---|---|---|---|---|---|
| KPNO | kp4m / test | 2010-08-13 | 5 | 190.9 | 1.73 | 27794 ± 125 | 5.364 ± 0.022 | -2.97 ± 0.06 | 2.10% | 2.28 |
| LAMOST | LAMOST | 1 | 141.9 | 2.50 | 27560 ± 172 | 5.465 ± 0.026 | -2.90 ± 0.06 | 1.37% | 0.99 | |
| NOT | NOT / ALFOSC_FASU | 2011-06-01 | 17 | 217.2 | 2.04 | 27488 ± 78 | 5.481 ± 0.013 | -3.01 ± 0.06 | 0.89% | 1.41 |
| WHT ★ | WHT / ISIS blue arm | 2010-07-28 | 2 | 203.0 | 1.82 | 27556 ± 66 | 5.475 ± 0.013 | -2.91 ± 0.05 | 0.84% | 1.42 |
★ 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] | 1217 |
| parallax error [%] | 3.7 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.078 (0.068–0.086) |
| … the dust map | 0.0848 (SFD×disk(f=0.91)) |
| log Θ [rad] | -11.094 +0.005 −0.005 |
| R [R☉] | 0.217 +0.009 −0.008 |
| M [M☉] | 0.515 +0.077 −0.067 |
| L [L☉] | 24.6 +2.2 −1.9 |
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 27556 K and log g 5.475 from WHT, with 36 of the fitted bands and reduced χ² 0.10. 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: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.
| reference | U. Heber, September 2026: KIC3527751_photometry_results1.pdf |
| his fit | with Reed (2011), 27900 +- 500 K / 5.37 +- 0.11: E(44-55) 0.086 +- 0.004, log Theta -11.095 +- 0.006, R 0.216 +0.010 -0.009, M 0.37 +0.12 -0.09, L 25.3, reduced chi2 1.00 |
| reproduced here | Reproduced here on the same prescription: E 0.080, log Theta -11.106, R 0.214, M 0.391, reduced chi2 1.47. Every quantity inside his error bar. |
| how they compare | The best-determined of the three, and the one that moves most. At the gravity here, 5.475 against his 5.37, the mass goes from 0.39 to 0.51 -- from well below canonical to slightly above it. Uli's 5.37 is essentially the KPNO fit here, 5.364, which is the worst of the four spectra of this star at 2.10 per cent residual; the other three cluster at 5.465 to 5.481. |
| note | The only one of the three bright enough (V = 14.8) for its 2MASS and WISE photometry to be trusted, and it shows: fifteen bands from 3500 A to 4.6 microns with no infrared excess and reduced chi2 1.4. The parallax is good to 4 per cent, so here the mass error really is set by the gravity. |
data/ holds the three mean spectra the fits here use -- meanallK.fits, meanallN.fits and meanallW.fits -- and the .spek products beside them. These are exactly the three spectra Foster et al. (2015) used. means/ holds the same three observations as they were sent in toroy.tgz, a bundle of 19 means of 9 Kepler-field stars reduced by J. Telting in January 2012 and sent in September 2026. Same telescopes, same NCOMBINE (5 KPNO, 17 NOT, 2 WHT), same dates; the difference is only that the copies in data/ were trimmed to 3689-5073 A to match the KPNO coverage, while these keep the full 3517-5073 A common grid. The fitted lines stop at H11, whose bluest continuum anchor is at 3741 A, so nothing in the 170 A of extra blue reaches the fit and the spectra here are not refitted from them. They are kept as the untrimmed source of record, and as what to start from if the line list is ever extended into the H12-H16 crowd for the high signal-to-noise spectra.