published, and under active reanalysis here — both the spectroscopy and the seismology are still moving
| reference | Ostensen et al. 2010, MNRAS 408, L51; Baran et al. 2015, A&A 577, A146 |
| title | 2M1938+4603: a rich, multimode pulsating sdB star with an eclipsing dM companion |
| Kepler data used | the 2010 letter used the 9.7 d COMMISSIONING light curve only; Baran et al. (2015) used 37 months and more than 16000 eclipses |
| pulsations | A rich pulsation spectrum from ~50 to 4500 microHz with p- and g-modes together, never before seen in a compact pulsator; orbital period 0.126 d with a strong reflection effect and grazing eclipses. Baran et al. (2015) found a 416 d eclipse-timing variation ascribed to a Jupiter-mass third body |
| spectra behind it | radial velocities were taken primarily with the B&C spectrograph on the 2.3 m Bok telescope at Kitt Peak, plus a few with the MMT Blue spectrograph, both with an 832 line/mm grating in second order. K1 = 65.7 +- 0.6 km/s |
| atmospheric parameters | Teff 29564 +- 106 K, log g 5.425 +- 0.009, log(NHe/NH) -2.36 +- 0.06, from Paper I (KepI) with metal-blanketed LTE models. The 2010 letter's own spectroscopy was for velocities, not for the atmosphere |
| the spectrum behind it | The MMT spectra quoted in the letter are not on disk. The Bok mean is (bok/, five spectra from 2008-06-14), but a Keck spectrum now supersedes it and there is nothing worth requesting. |
| survey archive | A LAMOST DR11 spectrum is here as LAMOST/, fitted in the LAMOST sample: 28222 +- 173 / 5.488 +- 0.024. Two further DR11 epochs are available. |
| how they compare | Four determinations, and they split by resolution rather than by grid. KepI 29564 / 5.425; Bok on Bamberg 29002 +- 44 / 5.513 +- 0.007 (chi2 5.2); LAMOST 28222 +- 173 / 5.488 +- 0.024 (chi2 0.96); KECK 28526 +- 32 / 5.296 +- 0.005 (chi2 1.38). Every low-resolution spectrum gives log g 5.42-5.51; the Keck spectrum alone gives 5.30, and it does so on the Bamberg grid to within 0.011 dex of the earlier fit on Uli's grid (5.2849 +- 0.0051). That 0.13-0.22 dex is the whole low-mass question. |
| rotational broadening | CONVROT is now ported to the Python fitter as spgrid.rot_operator, so the model is convolved with the real limb-darkened rotation profile G(x) = C1*sqrt(1-x^2) + C2*(1-x^2) whose half width D = (v/c)*lambda GROWS WITH WAVELENGTH -- 0.95 A at the Balmer limit against 1.67 A at H-alpha for this star, which no single Gaussian can do. Replacing the 1.89 A Gaussian stand-in with it moves Teff by +130 K and log g by +0.025 dex. With the profile right, vsini can be fitted: chi-square minimises at 95 km/s rather than the 76.6 the earlier fit assumed, though the curve is shallow (1.3834 against 1.3912). log g runs 5.285 to 5.310 across vsini 70-115 km/s, so the low gravity does not depend on the choice. |
| synchronous rotation? | For P_orb = 0.126 d and the radius implied by log g 5.30 with a canonical 0.47 Msun, synchronous rotation predicts v sin i ~ 96 km/s at the i ~ 70 deg the grazing eclipses require -- which is where the fitted 95 km/s lands. A consistency check rather than a proof: the radius depends on the very gravity being fitted, and the chi-square curve is shallow. |
| which spectrum to quote | The automatic rule takes the smallest per-pixel residual, which here picks LAMOST: at 0.02 A/px the Keck spectrum resolves its own noise and scores 1.75% against LAMOST's 1.02%. That is an artefact of sampling, not of quality -- Keck constrains log g five times better (+-0.005 against +-0.024) and is the only spectrum that resolves the rotation. Quote KECK. |
| note | WORK IN PROGRESS, spectroscopically and asteroseismically. This is the Toby project's own star and both analyses are still moving: the Keck gravity implies a low-mass post-RGB primary rather than a canonical EHB star, and the seismic side is being reworked from scratch. The 2010 letter presented it simply as an interesting target for Kepler -- which has turned out truer than anyone expected. |
Paper: Ostensen10_2M.pdf, Baran15b.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 |
|---|---|---|---|---|---|---|---|---|---|---|
| BOK | 1 | nan | 9.00 | 29002 ± 44 | 5.513 ± 0.007 | -2.26 ± 0.02 | 1.14% | 5.21 | ||
| KECK ★ | 1 | 96.5 | 0.10 | 28562 ± 33 | 5.306 ± 0.005 | -2.08 ± 0.01 | 1.78% | 1.44 | ||
| LAMOST | LAMOST | 1 | 268.9 | 2.50 | 28222 ± 172 | 5.488 ± 0.024 | -2.28 ± 0.05 | 1.02% | 0.96 |
★ 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] | 404 |
| parallax error [%] | 1.3 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.060 (0.048–0.072) |
| … the dust map | 0.0657 (SFD×disk(f=0.48)) |
| log Θ [rad] | -10.614 +0.006 −0.007 |
| R [R☉] | 0.218 +0.004 −0.004 |
| M [M☉] | 0.350 +0.045 −0.040 |
| L [L☉] | 28.4 +1.4 −1.3 |
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 28562 K and log g 5.306 from KECK, with 32 of the fitted bands and reduced χ² 0.06. 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, SDSS:g/SDSS:g', SDSS:i/SDSS:i', SDSS:r/SDSS:r', SDSS:u, WISE:W3, WISE:W4, GAIA/GAIA3:G, GAIA/GAIA3:Gbp, GAIA/GAIA3:Grp, SDSS:g, SDSS:r, SDSS:i, SDSS:z, SDSS:u/SDSS:u', SDSS:z/SDSS:z', Johnson:U, Johnson:V, Cousins:U, 2MASS:J, 2MASS:H, 2MASS:Ks, WISE:W1, WISE:W2.
A cool companion and extra reddening both redden the model, so the reddening is HELD rather than fitted -- at the one-star value where that agreed with the dust map, and at the map's value where it did not, since there the disagreement IS the companion.
| companion Teff [K] | 3500 |
| … log g (held) | 4.50 |
| R1 [R☉] | 0.2168 |
| R2 [R☉] | 0.0000 |
| main-sequence R at that T [R☉] | 0.360 |
| R2 over that | 0.00 |
| Δχ² over one star | 0.0 |
| reduced χ² | 0.41 |
| excess over one star | 0.6 sigma on WISE:W1 |
| bands put back for it | 2MASS:J, 2MASS:H, 2MASS:Ks, WISE:W1, WISE:W2 |
| reddening | 0.060 (held) |
| verdict | rejected |
Not adopted. the fit is not improved enough to buy two more parameters (dchi2 0, needs 20)
keck/ and bok/ are the working directories the earlier fits were made in,
copied here and kept as they were run, each with the line list of its era.
Neither holds an sp.spek, so fitk1 does not read them.
keck/ the Keck spectrum (keck3.spek, 0.02 A/px, 3502-6308 A) and the 2026
fit made on Uli's grid with vsini = 76.6 km/s: 29324 +- 35 K,
log g 5.2849 +- 0.0051, log n(He)/n(H) -2.042. keck.spek and
keck2.spek beside it cover only 3761-5161 A but at higher S/N.
bok/ the Bok 2.3 m B&C mean of five spectra from 2008-06-14, and its
2008 fit: 30442 +- 54 K, log g 5.444 +- 0.013.
The live directories are KECK/, BOK/ and LAMOST/, all linked to the master.
The MMT spectra the 2010 letter mentions are not on disk anywhere, but the
Keck spectrum supersedes both them and the Bok mean for atmospheric work,
so there is nothing to request.