The Spectrum of Sirius

Sirius at SIMBAD

At first the Blamer lines to confirm the spectral class A:

sirbalm.gif
Instrument: NESSIE4,    Date: Feb-Mar 2001

At a first glance the spectrum looks a little bit noisy compared to Vega. But Sirius belongs to a special group of A-type stars the Am stars. Sirius is a moderate member of this group with not so strong metallic lines.

Ok. Now lets stroll through the spectrum and see what we find.

sir38to41.gif

Our CCD becomes rapidly insensitive below 4000 Å. We think the emissions inside CaII and H10 are rather noise then signal. Anyway CaII at 3933 is weak due to the high temperature of the photosphere of Sirius.

A detailed view onto the region between H-gamma and H-beta

some lines between H-gamma and
H-beta

sir40to50.gif
The relation of 4383 and 4417 to 4481 is luminousity sensitive. We see the stronger blends 4383-85 Å (FeI,II), 4417 Å (FeII,TiII) in super giant Deneb.

Sirius vs. Deneb

sir48to67.gif

We use the region 4900 Å to 5500 Å to compare the abundances of metalls in Sirius and Vega.

metallicity of Sirius vs. Vega

sir64to76.gif

sir75to84.gif

sir84to89.gif
Besides the Paschen series there is also an interesting temperature sensitive pattern. The CaII triplett at 8498, 8542 and 8662 Å shows a negative temperature sensitivity. See the triplett in the solar spectrum!

Literature used to discuss the spectrum of Sirius:
Jaschek&Jaschek: The Classification of Stars
Weaver, Wm.B., Torres-Dodgen, A. 1995, ApJ, 446, 300-317
Sandakane, K., 1989, Pupl.Astron.Soc.Japan 41, 279-288
Gehlich, U.K., 1696, Astron. & Astrophys. 3, 169-178

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