a detailed study with both a full pulsation analysis and dedicated spectroscopy
| reference | Baran et al. 2016, A&A 585, A66 |
| title | A subsynchronously rotating pulsating subdwarf B star in a short-period binary with a white dwarf companion |
| Kepler data used | discovered in the survey phase (Q2 long cadence, Q2.3 short cadence) and analysed on the long series thereafter |
| pulsations | 61 periods, with rotationally split multiplets and an equally spaced period sequence; both features fed the mode identification. The binary and rotation periods together show the sdB to be SUBSYNCHRONOUS |
| orbit | P = 1.56 d with a white-dwarf companion; K1 = 57(3) km/s, with the orbital photometric signal dominated by Doppler boosting |
| spectra behind it | 35 radial-velocity measurements taken 2010-2012: two with WHT/ISIS R600B and a 1.0 arcsec slit, twenty-five with NOT/ALFOSC between May 2011 and September 2012 at 0.5 arcsec, and eight with the KPNO 4-m Mayall (RC-Spec/F3KB, kpc-22b) on 30 September and 1 October 2012. For the atmosphere they built one orbit-corrected mean per observatory -- 2 WHT, 19 NOT, 6 KPNO -- then convolved all three to 2.2 A and combined them to S/N ~ 110 for the NLTE fit |
| atmospheric parameters | NLTE Teff 27440 +- 120 K, log g 5.382 +- 0.019, log(nHe/nH) -2.57 +- 0.05. Light metals subsolar and Fe near solar; N enriched with C and O low, resembling CNO-cycle equilibrium; Mg and Si also measured. N/O = 4.28 |
| earlier values | An earlier LTE fit with Heber's metal-blanketed models gave 26800 +- 500 / 5.37 +- 0.08 / -2.8 +- 0.2, which is what the target list carried; superseded |
| the spectrum behind it | Found. The paper's own words for its LTE comparison fit are 'the new high-S/N orbit-corrected mean spectra ... the spectrum from each observatory separately', and those three means arrived in September 2026, built 2014-09-15: KPNO/ from 6 spectra, NOT/ from 19 and WHT/ from 2, each shifted to rest on the 1.56 d orbit before co-adding. They are the spectra behind 26717 / 5.340 / -2.660. The NLTE Table 2 value is one step further on -- all three convolved to 2.2 A and combined into a single S/N ~ 110 spectrum -- and that single combination is not itself a file here, but it is made of these. The 35 RVs include 6 NOT and 2 KPNO spectra that did not go into the means; those individual frames are still not on disk. WHT0 here is the earlier 2009 R300B classification spectrum, not one of the 35. |
| how they compare | The paper fitted these same three means twice and so did this project, which makes the grids directly comparable. Baran et al., Heber et al. (2000) LTE, each observatory separately and a weighted mean of the three: 26717 +- 70 / 5.340 +- 0.010 / -2.660 +- 0.020. Here on Bamberg v25, the same three spectra weighted the same way: 26493 +- 52 / 5.448 +- 0.009 / -2.536 +- 0.025. That is -224 K, +0.108 dex in gravity and +0.124 dex in helium. The gravity offset is the one to remember: Pippin gives +0.10 to +0.12 dex between the same two grids on Kern's two means, so across two stars and five spectra Bamberg reads about a tenth of a dex more gravity than Heber's LTE grid. The published NLTE value is 950 K hotter than either LTE fit, which is the LTE-NLTE step and not a grid difference |
| rotational broadening | Baran et al. assumed zero rotation, on the general argument that sdB rotation velocities are below 10 km/s (Geier & Heber 2012); at 2.2 A that assumption cannot be tested here either |
| note | A dedicated spectroscopic analysis with abundances as well as a full pulsation analysis, so this is a baseline reference. Its subsynchronous result joins Pablo et al. (2012) on Merry and Rorimac -- the same question the Toby project asks of 2M1938+4603. |
Paper: Baran16.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 | 2012-10-01 | 6 | 90.8 | 1.77 | 26885 ± 192 | 5.405 ± 0.032 | -2.55 ± 0.07 | 1.93% | 1.46 |
| NOT ★ | NOT / ALFOSC_FASU | 2011-05-31 | 19 | 263.8 | 2.24 | 26441 ± 60 | 5.456 ± 0.010 | -2.51 ± 0.03 | 0.78% | 1.77 |
| WHT | WHT / ISIS blue arm | 2010-07-28 | 2 | 109.4 | 1.98 | 26553 ± 124 | 5.434 ± 0.021 | -2.63 ± 0.06 | 1.31% | 1.25 |
| WHT-uncorrected | WHT / ISIS blue arm | 2010-07-28 | 2 | 96.2 | 1.92 | 26552 ± 128 | 5.428 ± 0.022 | -2.62 ± 0.07 | 1.37% | 1.19 |
| WHT0 | WHT / ISIS blue arm | 2009-07-15 | 1 | 32.5 | 2.48 | 27127 ± 333 | 5.499 ± 0.059 | -2.53 ± 0.17 | 3.37% | 1.40 |
| WHT1 | WHT / ISIS blue arm | 2010-07-28 | 1 | 58.4 | 1.60 | 26761 ± 179 | 5.406 ± 0.031 | -2.69 ± 0.12 | 2.05% | 1.34 |
| WHT2 | WHT / ISIS blue arm | 2010-07-28 | 1 | 60.3 | 1.80 | 26529 ± 215 | 5.514 ± 0.038 | -2.69 ± 0.12 | 4.41% | 2.16 |
★ 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] | 2271 |
| parallax error [%] | 8.3 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.114 (0.098–0.128) |
| … the dust map | 0.0763 (SFD×disk(f=1.00)) |
| log Θ [rad] | -11.380 +0.009 −0.008 |
| R [R☉] | 0.210 +0.019 −0.017 |
| M [M☉] | 0.461 +0.107 −0.085 |
| L [L☉] | 19.4 +3.8 −3.0 |
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 26441 K and log g 5.456 from NOT, with 28 of the fitted bands and reduced χ² 0.14. 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:W2, 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, WISE:W1 — the last of these was not excluded by rule but clipped, sitting beyond five sigma of a model that fits its neighbours.
means/ holds two sets of mean spectra and the archives they came in. Will.tgz, September 2026, built 2014-09-15: meanKnoOrbit.fits, meanNnoOrbit.fits and meanWnoOrbit.fits, one per observatory, each shifted to rest on the 1.56 d orbit before co-adding. These are the spectra Baran et al. (2016) call "the new high-S/N orbit-corrected mean spectra" and fitted "from each observatory separately" for their LTE comparison value. They are KPNO/, NOT/ and WHT/ here. Their grid runs 3605-5051 A at 0.765 A/px -- narrower than the batch below, because the orbital shift eats the ends. kic07664467-meanN.fits and -meanW.fits, from toroy.tgz, built January 2012: means of 7 NOT and 2 WHT spectra with the orbit left in. The NOT one is superseded outright by the 19-spectrum corrected mean and is not fitted. The WHT one is kept and fitted as WHT-uncorrected/, because it and WHT/ are the SAME two spectra of 2010-07-28, one with the orbital motion removed and one without, and that is a controlled test of what the correction is worth. The answer is: nothing here. Teff moves 1 K and log g 0.005 dex. Both WHT spectra were taken on one night, so there was little orbital phase to smear over; at K1 = 57 km/s a full spread would be +-0.8 A at H-gamma, comparable to the resolution, so the test says the correction did not matter for THIS pair rather than that it never matters. NOT/ is the best spectrum of the star by some way -- 19 spectra, S/N 264, residual 0.78% against 1.3-4.4% for everything else -- so it is the one the sample table quotes. wht0/, wht1/ and wht2/ are the original fitprof22 working directories, kept as they were run. They hold no sp.spek, so fitk1 does not read them. wht0/J18561+4319B.fits (and the .spek beside it) is a failed extraction -- median flux -50, essentially noise; the usable product of that observation is wht0/J18561+4319.spek, which is what WHT0/ is extracted from. WHT0 is the 2009 R300B classification spectrum and is not one of the paper's 35. wht1 and wht2 are IRAF multispec files, so only band 1 is the spectrum.