a detailed study with both a full pulsation analysis and dedicated spectroscopy
| reference | Ostensen et al. 2012, ApJL 753, L17 |
| title | KIC 1718290: a helium-rich V1093-Her-like pulsator on the blue horizontal branch |
| Kepler data used | one year |
| pulsations | Rich spectrum of low-amplitude modes, periods 1-12 h, most following a regular 276.3 s spacing |
| spectra behind it | WHT/ISIS, flux calibrated against Feige 67 observed the same night; a mean NOT spectrum was also fitted |
| atmospheric parameters | Teff 22100 K, log g 4.72, log N(He)/N(H) -0.45 (abstract); the WHT fit gives 22350 +- 200 / 4.75 +- 0.03 / -0.49 +- 0.04 and the NOT mean 21796 +- 144 / 4.67 +- 0.03 / -0.40 +- 0.04 |
| the spectrum behind it | The flux-calibrated WHT spectrum is here, with the Feige 67 calibration work beside it, and the NOT mean as well. |
| note | A Letter, and only one year of Kepler data, but it carries a real spectroscopic analysis including the flux calibration. The first g-mode pulsator found on the classical blue horizontal branch. |
Paper: Ostensen12b.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 |
|---|---|---|---|---|---|---|---|---|---|---|
| LAMOST | LAMOST | 2018-05-17 | 1 | 79.3 | 2.50 | 23154 ± 327 | 4.955 ± 0.044 | -0.55 ± 0.03 | 2.64% | 1.41 |
| WHT | WHT / ISIS blue arm | 2010-07-03 | 1 | 82.2 | 1.32 | 23258 ± 154 | 4.905 ± 0.019 | -0.58 ± 0.02 | 2.13% | 1.35 |
| WHT-raw ★ | WHT / ISIS blue arm | 2010-07-03 | 1 | 81.8 | 1.32 | 23202 ± 153 | 4.917 ± 0.019 | -0.59 ± 0.02 | 2.12% | 1.36 |
★ 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] | 2715 |
| parallax error [%] | 6.5 (per cent; the mass error is twice this) |
| E(44−55) [mag] | 0.220 (0.210–0.230) |
| … the dust map | 0.1551 (SFD×disk(f=0.98)) |
| log Θ [rad] | -11.093 +0.005 −0.005 |
| R [R☉] | 0.486 +0.034 −0.030 |
| M [M☉] | 0.713 +0.138 −0.114 |
| L [L☉] | 61.6 +9.4 −7.7 |
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 23202 K and log g 4.917 from WHT-raw, with 35 of the fitted bands and reduced χ² 0.24. 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.
| how they compare | The one blue horizontal branch star in the sample, and it behaves like one: R = 0.53 Rsun, three times the subdwarfs around it. The fitted reddening runs high against the maps (0.263 against 0.155), so the radius is probably overstated and with it the 0.85 Msun mass. |
wht/ and wht/std/ are the original 2012 fitprof22 working directories, kept as they were run: wht/ holds the published fit (Teff 22351, log g 4.755, log n(He)/n(H) -0.486 on the Uli grids) and wht/std/ the flux calibration behind it -- Feige 67 fitted as a 58 kK sdO so the observed/model ratio gives the instrument response, plus the 15th-order flxcor polynomial. Each carries the line list of its own era, and chidel.dat here is the file those two link to. Neither holds an sp.spek, so fitk1 does not read them. The live directories are WHT/ (the flux-calibrated spectrum, flxcor.fits -- the one the published fit used), WHT-raw/ (the same night with no flux calibration) and LAMOST/ (DR11, 2018). All three link to the master.