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Adelard NOT

b4b5 · ALFOSC_FASU · 2012-05-17

32.6S/N per pixel
4.41%residual rms
4.50 Åresolution
?spectra combined
sdOBclass

The fit

fitTeff [K]log glog n(He)/n(H)Zreduced χ²
three parameters24094 ± 6325.479 ± 0.083-2.95 ± 0.34held 01.12
four parameters24388 ± 5865.530 ± 0.097-2.94 ± 0.391.00 ± 0.581.10

Observed minus model scatters by 4.41% of the continuum over the fitted lines, worst on Hκ (7.1%), Hθ (4.7%). 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+0.320
log g ↔ Z+0.363
helium ↔ Z+0.057
Teff ↔ log g+0.623

Core shifts, line by line

Hβ, Hγ and Hδ give +136.1 km/s between them, so the star's radial velocity is -136.1 km/s; they scatter by 13.5 km/s about it.

lineλ0shift [Å][km/s]
Hβ4861.32+2.48+152.9beyond any plausible radial velocity
Hγ4340.46+1.96+135.4beyond any plausible radial velocity
Hδ4101.73+1.64+119.9
Hε3970.07+1.20+90.6
Hζ3889.05+1.59+122.6beyond any plausible radial velocity
Hη3835.38+0.68+53.2
Hθ3797.90+1.82+143.7beyond any plausible radial velocity
Hι3770.63+1.19+94.6
Hκ3750.15+6.99+558.8model slid +7.0 Å onto a noise minimum
He II 46864685.70+8.72+557.9model slid +8.7 Å onto a noise minimum
He I 44724471.60+6.99+468.6model slid +7.0 Å onto a noise minimum
He I 40264026.29+1.86+138.5beyond any plausible radial velocity
He I 49224921.93-3.31-201.6beyond 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-0.100.000.10-500+50Hγ1.9%
0.501.00observed3p model4p model-0.100.000.10-500+50Hδ1.6%
0.501.00observed3p model4p model-0.100.000.10-200+20+40Hε1.3%
1.00observed3p model4p model-0.100.000.10-200+20Hζ0.8%
0.600.801.00observed3p model4p model-0.100.000.10-200+20Hη0.5%
0.801.00observed3p model4p model-0.100.000.10-200+20Hθ0.8%
0.801.00observed3p model4p model-0.100.000.10-100+10Hι1.1%
1.00observed3p model4p model-0.100.000.10-100+10Hκ0.8%
0.901.00observed3p model4p model-0.050.000.05-200+20He II 46860.0%
0.901.00observed3p model4p model-0.100.000.10-200+20He I 44720.1%
1.00observed3p model4p model-0.050.000.05-200+20He I 40260.2%
0.901.00observed3p model4p model-0.100.000.10-200+20He I 49220.1%

Where it came from

objectb4b5
telescopeNOT
instrumentALFOSC_FASU
grism / gratingGrism_#16
slitSlit_1.0
date2012-05-17T04:24:52.231
exposure [s]3600.0
airmass1.0171505632329
observerMattias-Ergon
pixels2052
range [Å]3528.61 5091.72
dispersion [Å/px]0.7621
S/N estimate32.6
FWHM from Ca II K [Å]4.50
Ca II K shift [Å]-0.98
W(He II 4686) [Å]0.181
W(He I 4471) [Å]0.418
source fileB5.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.