a detailed study with both a full pulsation analysis and dedicated spectroscopy
The published spectrum is not on disk here. Only the Bok pair is missing, and it is the pair the quoted value rests on: Charpinet et al. derived the NLTE parameters from two 30-minute Bok spectra taken on 2010 June 15 and 17 and combined to R ~ 580, and no Bok spectrum of this star is on disk -- ask S. Charpinet, or E. M. Green who took them. Kern et al.'s spectroscopy is all here, and so now is the analysis: the working directory that produced it arrived in September 2026 as Pippin.tgz and is here as not2016/ and wht2016/, with its own line list, its fit output and the panels of the paper's Fig. 1. The two means it fitted are the same two this project holds -- re-made a week later on a grid trimmed to 3550 A, agreeing with the 3517 A copies to 0.05 per cent of the continuum on the NOT and 0.016 on the WHT, within 0.04 A in wavelength. NOT/ and WHT/ here are those spectra.
| reference | Charpinet et al. 2011, A&A 530, A3; Baran 2012, AcA 62, 179; Kern et al. 2017, MNRAS 465, 1057 |
| title | Charpinet et al.: Deep asteroseismic sounding of the compact hot B subdwarf pulsator KIC 02697388 from Kepler time series photometry. Kern et al.: Kepler observations of the pulsating subdwarf B star KIC 2697388: the detection of converging frequency multiplets in the full data set |
| Kepler data used | Charpinet et al. had the ~27 d exploratory run Q2.3 only; Kern et al. (2017) analysed the full short-cadence set, 1147.5 d at a 91.4 per cent duty cycle |
| pulsations | Charpinet et al. forward-modelled the Q2.3 spectrum to an objective mode identification and a seismic model. Kern et al. (2017) detected 253 periodicities in the full set, identified 89 per cent of them (42 with l >= 3), and found a rotation period of ~42 d. Their unique result is that the splittings of every l >= 2 multiplet DECREASE over the three years; on that trend those multiplets would be singlets within a decade |
| spectra behind it | Charpinet et al.: two 30-minute Bok spectra combined to R ~ 580, analysed with NLTE model atmospheres. Kern et al.: 21 spectra at R ~ 2000-2500 -- 3 WHT/ISIS R600B at a 1.0 arcsec slit on 2010 July 27-28 (S/N 87-114) and 18 NOT/ALFOSC grism #16 at 0.5 arcsec on ten nights across 2011 May-July (S/N 33-63), exposures 500-900 s, arc-line resolutions 1.7 and 2.2 A -- averaged per telescope to S/N ~ 190 each |
| atmospheric parameters | Charpinet et al., Table 6, marked 'from spectroscopy': Teff 25395 +- 227 K, log g 5.500 +- 0.031, log N(He)/N(H) -2.767 +- 0.122 (NLTE; the quoted errors are formal). This is what the sample table quotes -- see 'how they compare' for why, and for the case against it |
| earlier values | An earlier LTE fit gave 23900 +- 300 / 5.32 +- 0.03 / -2.9 +- 0.1 (Ostensen et al. 2010, KepI), which is what the target list carried before Charpinet et al. |
| how the published fit was made | What the 2016 directory shows about how Kern et al.'s numbers were made, and how it differs from the fit here. It used Uli's grid with only TWO helium models, log(He/H) -3.00 and -2.00, interpolating between them for the -2.91 it reports; a temperature grid of 22500-30000 K in steps of 2500 and gravities 5.0, 5.25, 5.5 and 6.0; the resolution held at the arc-line values, 2.20 A for the NOT and 1.70 A for the WHT; and 'radvel', ONE imposed velocity (26 and 8 km/s) rather than a shift found for each line. Eleven lines were fitted -- H-beta to H10 and He I 4472, 4026, 4713 and 4922 -- with no H11 and no He II 4686. This project fits twelve on Bamberg v25 with six helium grids, sliding windows and a free shift per line: H-beta to H11, He II 4686 and He I 4472, 4026 and 4922, so H11 and He II 4686 are in here and were not there, and He I 4713 was there and is not here |
| a caution | One caution if these numbers are ever quoted from the directory rather than the paper: they do not quite match. The fit.out files give NOT 23239 +- 150 / 5.265 +- 0.020 / -2.913 +- 0.029 and WHT 24165 +- 77 / 5.310 +- 0.012 / -2.923 +- 0.023, against the published 23390 +- 118 / 5.29 +- 0.015 / -2.911 and 24262 +- 86 / 5.34 +- 0.011 / -2.913. That is about 150 K and 0.03 dex, and both files predate submission (2016 April 22 and July 31, the paper 2016 August 12), so the printed table came from a run that is not the one preserved here. On a grid stepped 2500 K and 0.25 dex, a small change of setup moves the interpolated answer by that much. Quote the paper |
| the spectrum behind it | Only the Bok pair is missing, and it is the pair the quoted value rests on: Charpinet et al. derived the NLTE parameters from two 30-minute Bok spectra taken on 2010 June 15 and 17 and combined to R ~ 580, and no Bok spectrum of this star is on disk -- ask S. Charpinet, or E. M. Green who took them. Kern et al.'s spectroscopy is all here, and so now is the analysis: the working directory that produced it arrived in September 2026 as Pippin.tgz and is here as not2016/ and wht2016/, with its own line list, its fit output and the panels of the paper's Fig. 1. The two means it fitted are the same two this project holds -- re-made a week later on a grid trimmed to 3550 A, agreeing with the 3517 A copies to 0.05 per cent of the continuum on the NOT and 0.016 on the WHT, within 0.04 A in wavelength. NOT/ and WHT/ here are those spectra. |
| how they compare | Four spectroscopic determinations of this star, and they split by resolution. Charpinet et al. (2011), 2 Bok spectra at R ~ 580, NLTE: 25395 +- 227 / 5.500 +- 0.031 / -2.767. Kern et al. (2017), the same two averages held here, LTE (Heber et al. 2000): WHT 24262 +- 86 / 5.34 +- 0.011 / -2.913, NOT 23390 +- 118 / 5.29 +- 0.015 / -2.911. Here on Bamberg v25: WHT 24434 +- 64 / 5.464 +- 0.008 / -2.89, NOT 23761 +- 117 / 5.391 +- 0.016 / -2.95. Ostensen et al. (2010): 23900 +- 300 / 5.32. Two points. First, this fit and Kern's agree on the same spectra to 172 K (WHT) and 371 K (NOT) in temperature and to 0.04 dex in helium, and both sit about 1000 K BELOW the R ~ 580 NLTE pair -- the same pattern Toby shows, where every low-resolution spectrum reads high. Second, both analyses find the same offset between the telescopes, WHT minus NOT = +872 K for Kern and +673 K here, so that split is in the spectra and not in the fitting. Log g is the exception: Bamberg gives 0.10-0.12 dex more gravity than Heber's LTE grid on the identical spectra |
| rotational broadening | Kern et al. report no rotational broadening; their 21 spectra give a radial-velocity scatter of rms 9.5 km/s with no periodic signal, which rules out short-period low-inclination orbits but is not accurate enough to rule out binarity altogether |
| which spectrum to quote | The table still quotes Charpinet et al. because it is the only paper that ADOPTS a single spectroscopic value for this star: Kern et al. call their two numbers 'a first estimate' and never combine them or carry them into the seismology. If the better DATA are to win instead -- 21 spectra at R ~ 2000-2500 against 2 at R ~ 580 -- then the published column should become Kern's, and the choice between his WHT and NOT values is the awkward part |
| note | The pulsation analysis is spread over three papers and the last one is the complete one. Charpinet et al. (2011) had 27 days; Baran (2012) had nine months, 148 frequencies and a rotation period of 45.6 +- 4.8 d; Kern et al. (2017) had all 1147.5 days, 253 frequencies and ~42 d. The spectroscopy runs the other way: the best DATA are Kern's 21 spectra, but the only single adopted value is Charpinet's, from two spectra at a twentieth of the resolution. |
Paper: Charpinet11.pdf, Kern17.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 | 2011-05-31 | 18 | 228.2 | 2.15 | 23762 ± 117 | 5.391 ± 0.016 | -2.95 ± 0.05 | 1.20% | 1.82 |
| NOT-2008 | NOT / ALFOSC_FASU | 2008-09-22 | 1 | 115.9 | 6.50 | 23768 ± 257 | 5.331 ± 0.035 | -2.75 ± 0.10 | 1.38% | 1.55 |
| WHT ★ | WHT / ISIS blue arm | 2010-07-27 | 3 | 274.1 | 1.85 | 24434 ± 64 | 5.464 ± 0.008 | -2.89 ± 0.03 | 0.74% | 2.04 |
| WHT1 | WHT / ISIS blue arm | 2010-07-27 | 1 | 110.6 | 1.67 | 24488 ± 135 | 5.478 ± 0.018 | -2.87 ± 0.06 | 1.30% | 1.57 |
| WHT2 | WHT / ISIS blue arm | 2010-07-28 | 1 | 109.7 | 1.53 | 24796 ± 144 | 5.455 ± 0.019 | -2.90 ± 0.06 | 1.24% | 1.12 |
| WHT3 | WHT / ISIS blue arm | 2010-07-28 | 1 | 114.4 | 1.47 | 24172 ± 142 | 5.423 ± 0.019 | -2.97 ± 0.07 | 1.11% | 1.34 |
| lamost | 1 | ? | 2.50 | 24076 ± 271 | 5.390 ± 0.034 | -2.84 ± 0.07 | 1.83% | 0.99 |
★ 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] | 1269 |
| parallax error [%] | 3.4 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.074 (0.064–0.084) |
| … the dust map | 0.1299 (SFD×disk(f=0.90)) |
| log Θ [rad] | -11.165 +0.005 −0.005 |
| R [R☉] | 0.193 +0.007 −0.007 |
| M [M☉] | 0.395 +0.058 −0.050 |
| L [L☉] | 11.9 +1.0 −0.9 |
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 24434 K and log g 5.464 from WHT, with 35 of the fitted bands and reduced χ² 0.72. 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.
means/ holds the two mean spectra of this star 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. The whole batch sits on one 3517-5073 A,
0.765 A/px scale, so the telescopes can be compared pixel for pixel. It
also holds Pippin.tgz, the April-July 2016 working directory behind Kern
et al. (2017), which arrived separately. Only the fitting material was
unpacked, into not2016/ and wht2016/; the tarball still carries the rest,
which is 11 MB of light-curve and Fourier figures (Pippin_all.eps and its
two zooms, kic02697388.ps) with no spectroscopy in them.
These two are the spectra behind Kern et al. (2017). That paper used
21 spectra -- 3 WHT and 18 NOT -- averaged per telescope, and these are
means of exactly 3 and 18, at 1.85 and 2.15 A against the 1.7 and 2.2 A
it quotes from its arc lines.
NOT/ mean of 18 NOT/ALFOSC grism #16 spectra taken on ten nights across
2011 May-July; the header date is the first of them.
WHT/ mean of 3 WHT/ISIS R600B spectra, 2010-07-27/28 -- the same three
that are also here singly as WHT1, WHT2 and WHT3. Its fit has a
residual of 0.74% against 1.1-1.3% for the singles, so it is the one
the sample table quotes.
Worth noting for calibration elsewhere: Kern et al. put both averages at
S/N ~ 190, while the local-scatter estimate in spec.info reads 228 and
274. On resampled means that estimator runs 20-45% high, because the
resampling correlates neighbouring pixels and the scatter it measures is
no longer the photon noise. The `snr_est` figures on these pages are
comparable with each other and should not be quoted against a published
signal-to-noise.
NOT-2008/ was called NOT until these arrived: the single 2008 KepI
classification spectrum at 6.5 A resolution, from
data/spek/kepler/KepI/J19091+3756_NOT/. It is kept because it is a
separate observation, and it is reassuring: at a quarter the
resolution it lands within 6 K of the new NOT mean.
not2016/ and wht2016/ are that 2016 directory as it arrived, with each
sp.spek renamed meanN.spek and meanW.spek so that fitk1 does not read
them. They brought NO new spectra: the FITS in them are the same two
means, re-made on 2012-01-24/25 on a grid trimmed to 3550 A, and they
agree with the 3517 A copies in means/ to 0.05 per cent of the continuum
on the NOT and 0.016 per cent on the WHT, within 0.04 A in wavelength and
0.8 per cent in flux scale. What they do bring is the analysis: the line
list it used, the fit output, and the panels of the paper's Fig. 1.
Their chidel.dat is that 2016 private list, kept as it was run -- this
note is what makes it legitimate to mkindex. It differs from the master
in more than windows: the fit used eleven lines, H-beta to H10 plus He I
4472, 4026, 4713 and 4922, with no H11 and no He II 4686, and it imposed
a single radial velocity rather than centring each line. See the target
page for the rest of the comparison.
lamost/ is a copied LAMOST working directory and is live.
NOTE: not/ and wht/ do NOT hold Pippin. Both contain
kic07668647-*-noOrbit.fits, byte-identical to the files in Primula/not and
Primula/wht -- KIC 7668647 = FBS 1903+432 = Primula, not KIC 2697388.
paper/ is misfiled the same way: Telting14.pdf is Primula's paper.
Nothing here was ever fitted from them: NOT-2008/ comes from
data/spek/kepler/KepI/J19091+3756_NOT/ and WHT1-3/ from
data/spek/kepler/K02697388/fits/.
The 2010 fits of the WHT trio used vsini = 29 km/s. The Python fitter
now has the CONVROT rotation profile, but at this resolution folding the
rotation into the instrumental profile instead moves Teff by 26 K and
log g by 0.004 dex, so the fits here leave it out.