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Fredegar NOT

b3b6 · ALFOSC_FASU · 2012-05-14

54.9S/N per pixel
2.86%residual rms
4.50 Åresolution
2spectra combined
sdBclass

The fit

fitTeff [K]log glog n(He)/n(H)Zreduced χ²
three parameters24845 ± 3365.356 ± 0.050-2.64 ± 0.11held 01.68
four parameters25055 ± 3275.442 ± 0.061-2.61 ± 0.121.00 ± 0.321.58

Observed minus model scatters by 2.86% of the continuum over the fitted lines, worst on Hκ (3.8%), Hθ (3.6%). That number, not the signal-to-noise, is what says whether the spectrum can carry a fourth parameter.

Correlations in the four-parameter fit

paircorrelation
Teff ↔ Z+0.304
log g ↔ Z+0.499
helium ↔ Z+0.097
Teff ↔ log g+0.750

Core shifts, line by line

Hβ, Hγ and Hδ give +171.6 km/s between them, so the star's radial velocity is -171.6 km/s; they scatter by 15.6 km/s about it.

lineλ0shift [Å][km/s]
Hβ4861.32+3.14+193.6beyond any plausible radial velocity
Hγ4340.46+2.32+160.2beyond any plausible radial velocity
Hδ4101.73+2.20+160.8beyond any plausible radial velocity
Hε3970.07+2.31+174.4beyond any plausible radial velocity
Hζ3889.05+2.11+162.7beyond any plausible radial velocity
Hη3835.38+2.08+162.6beyond any plausible radial velocity
Hθ3797.90+2.86+225.8beyond any plausible radial velocity
Hι3770.63+2.40+190.8beyond any plausible radial velocity
Hκ3750.15+1.53+122.3beyond any plausible radial velocity
He II 46864685.70-0.61-39.0
He I 44724471.60+3.32+222.6beyond any plausible radial velocity
He I 40264026.29+2.56+190.6beyond any plausible radial velocity
He I 49224921.93+2.84+173.0beyond any plausible radial velocity

Each line is centred independently: the fitter finds its core with a parabola and slides the model there. The sign is the fitter's, opposite to the star's motion. Lines far from the Balmer mean above are not measuring a velocity — near the Balmer jump the series crowds and pulls the apparent core blueward, and a weak line has no core to find at all.

Spectrum

shaded: the intervals the fit used ·  │ a cancelled pixeldrag on either panel to zoom · dbl-click or Esc to reset · arrows to pan

The whole reduced spectrum. Shaded bands are the intervals the fit used; drag on either panel to zoom.

Line by line

residuals

Offset from the line centre in Ångström across, normalised flux up. The strip under each profile is observed minus model for whichever fit the buttons select; they all switch together and share a vertical scale.

0.600.801.00observed3p model4p model-0.050.000.05-500+50Hβ2.0%
0.501.00observed3p model4p model-0.050.000.05-500+50Hγ1.8%
0.501.00observed3p model4p model-0.050.000.05-500+50Hδ1.5%
0.501.00observed3p model4p model-0.100.000.10-200+20+40Hε1.2%
0.600.801.00observed3p model4p model-0.050.000.05-200+20Hζ0.6%
0.801.00observed3p model4p model-0.100.000.10-200+20Hη0.7%
0.801.00observed3p model4p model-0.100.000.10-200+20Hθ1.3%
0.801.00observed3p model4p model-0.100.000.10-100+10Hι1.6%
0.901.001.10observed3p model4p model-0.050.000.05-100+10Hκ1.2%
0.951.001.05observed3p model4p model-0.050.000.05-200+20He II 46860.1%
0.901.00observed3p model4p model-0.050.000.05-200+20He I 44720.1%
0.951.001.05observed3p model4p model-0.050.000.05-200+20He I 40260.3%
0.951.001.05observed3p model4p model-0.0500.0000.050-200+20He I 49220.1%

Where it came from

objectb3b6
telescopeNOT
instrumentALFOSC_FASU
grism / gratingGrism_#16
slitSlit_1.0
date2012-05-14T04:17:59.837
exposure [s]3000.0
spectra combined2
airmass1.0263339004701
observerAxl Rose
pixels1942
range [Å]3600.00 5079.62
dispersion [Å/px]0.7623
S/N estimate54.9
FWHM from Ca II K [Å]4.50
Ca II K shift [Å]-1.98
W(He II 4686) [Å]0.121
W(He I 4471) [Å]0.415
source fileB3.fits

The resolution is measured from the interstellar Ca II K line, which is not in the star, so its width is the instrumental profile. It is an upper limit: an unresolved interstellar line can still be several velocity components. The same fit gives the wavelength shift, which is the zero point only in so far as the cloud sits near rest.