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Fredegar NOT-2

b3b6 · ALFOSC_FASU · 2012-05-30

38.2S/N per pixel
3.76%residual rms
4.50 Åresolution
?spectra combined
sdBclass

The fit

fitTeff [K]log glog n(He)/n(H)Zreduced χ²
three parameters25306 ± 4635.400 ± 0.071-2.51 ± 0.16held 01.28
four parameters25363 ± 4595.473 ± 0.086-2.48 ± 0.181.00 ± 0.491.22

Observed minus model scatters by 3.76% of the continuum over the fitted lines, worst on Hκ (5.5%), Hθ (4.9%). 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+0.207
log g ↔ Z+0.450
helium ↔ Z+0.094
Teff ↔ log g+0.684

Core shifts, line by line

Hβ, Hγ and Hδ give +175.4 km/s between them, so the star's radial velocity is -175.4 km/s; they scatter by 20.9 km/s about it.

lineλ0shift [Å][km/s]
Hβ4861.32+3.32+204.7beyond any plausible radial velocity
Hγ4340.46+2.37+163.7beyond any plausible radial velocity
Hδ4101.73+2.16+157.9beyond any plausible radial velocity
Hε3970.07+2.32+175.2beyond any plausible radial velocity
Hζ3889.05+2.52+194.3beyond any plausible radial velocity
Hη3835.38+1.82+142.3beyond any plausible radial velocity
Hθ3797.90+3.39+267.6model slid +3.4 Å onto a noise minimum
Hι3770.63+2.54+201.9beyond any plausible radial velocity
Hκ3750.15+1.48+118.3
He II 46864685.70-0.97-62.1
He I 44724471.60+3.05+204.5beyond any plausible radial velocity
He I 40264026.29+2.03+151.2beyond any plausible radial velocity
He I 49224921.93+3.26+198.6beyond 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.

0.501.00observed3p model4p model-0.100.000.10-500+50Hβ2.0%
0.501.00observed3p model4p model-0.050.000.05-500+50Hγ1.8%
0.501.00observed3p model4p model-0.050.000.05-500+50Hδ1.6%
0.501.00observed3p model4p model-0.050.000.05-200+20+40Hε1.2%
1.00observed3p model4p model-0.100.000.10-200+20Hζ0.6%
1.00observed3p model4p model-0.100.000.10-200+20Hη0.6%
0.801.00observed3p model4p model-0.100.000.10-200+20Hθ1.1%
0.801.00observed3p model4p model-0.100.000.10-100+10Hι1.3%
0.801.00observed3p model4p model-0.100.000.10-100+10Hκ0.9%
1.00observed3p model4p model-0.050.000.05-200+20He II 46860.2%
0.901.001.10observed3p model4p model-0.050.000.05-200+20He I 44720.1%
1.00observed3p model4p model-0.050.000.05-200+20He I 40260.3%
1.00observed3p model4p model-0.050.000.05-200+20He I 49220.1%

Where it came from

objectb3b6
telescopeNOT
instrumentALFOSC_FASU
grism / gratingGrism_#16
slitSlit_1.0
date2012-05-30T03:58:59.606
exposure [s]3600.0
airmass1.0123691853279
observer44-415
pixels2052
range [Å]3528.24 5091.39
dispersion [Å/px]0.7621
S/N estimate38.2
FWHM from Ca II K [Å]4.50
Ca II K shift [Å]-1.92
W(He II 4686) [Å]-0.078
W(He I 4471) [Å]0.560
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.