Page 61 - spectroscopic-atlas-5_0-english_Neat

Spectroscopic Atlas for Amateur Astronomers 61

Here it was also confirmed, that the spectrum, taken in a wider area of the NGC 2261 neb-
ula, looks similar to a profile, recorded very close to R Monocerotis. Thus NGC 2261 is ap-
parently rather a reflection than an emission nebula. The quality of the obtained noisy pro-
files however is insufficient for this publication. The line identification is inter alia based on
[2] and [270].

This highly interesting object is also very popular amongst astrophotographers who record
the short-term brightness variations in spectacular series of images. On January 26, 1949
NGC 2261 became famous, because Edwin Hubble himself photographed this nebula as
the official First Light Object of the new 5m telescope at Mount Palomar Observatory!

Table 18: T Tauri HD 284419, Prototype of the T Tauri Stars

T Tauri (approx. 462 ly, [Loinard et al.]) is a Classical T Tauri Star CTTS with highly intense
emission lines. This clearly demonstrates here the EW value of Hα: ‫ܹܧ‬ுఈ ≈ −87Å. At first
glance, the two profiles of Table 17 and 18 look very similar. The Fe II (42) multiplet how-
ever is here much weaker, but the Ca II emission significantly stronger. T Tauri is classified
as G5 Ve, much later than Type A. This can only be recognized here at the CH absorption
band (λ ~4300).

A highly interesting detail are the forbidden [O I] line, the strikingly intense sulphur lines [S
II] and the Hγ emission, which at the time of recording on March 27, 2012 appeared as In-
verse P Cygni profiles! These indicate large-scale contraction movements within the accre-
tion disk, headed towards the star – this in contrast to the normal P Cygni profiles, which
are always a reliable sign for an expansion. The Doppler analysis showed here contraction
velocities of some 600 km/s (formula and example see Table 2).

According to AAVSO the apparent brightness of the object at the
time of recording was ~10m. The spectrum in Table 18 was taken
with DADOS and the 25μm slit; exposure time 3x724 seconds: Atik
314L, –10°C, 2x2 binning mode. As for Table 17, it was here also
necessary, to subtract the disturbing light pollution spectrum from
the T Tauri signal. At T Tauri, as a by-product of this star birth, a
closely neighbouring Herbig Haro object is to observe. Here it is the
variable nebula NGC1555, named after John Russell Hind (1823-
95) visible in large telescopes next to T Tauri (image: CDS).

Table 19: FU Orionis, G3 Iav + K, [500], Vvar= ~+9.6m and γ Leonis, Algieba, K0 IIIb+G7III

Spectral comparison of the protostar FU Orionis (approx. 1300 ly, [289]), with the K0 IIIb
giant γ Leonis (approx. 126 ly). Recording data with C8/DADOS/Atik 314L+: 25μm slit,
8x600 seconds, 2x2 binning mode, –20°C, including subtraction of the light pollution. In
the short-wave range the "Fuor" spectra look generally like those of F–G Supergiants, but in
the near-infrared rather like those of K-giants. In comparison to γ Leonis (K0 IIIb), this is
easily recognisable here and is also expressed by the spectral class of G3 Iav + K. In com-
parison with the γ Leonis profile we see the following striking differences:

– At FU Orionis the Hα line forms a distorted P-Cygni profile. Typically, the
red shifted emission part appears here strongly stunted [286], [290].

– The strong, broad absorption of lithium Li I at λ 6708 shows, that FU
Orionis must necessarily be a very young object, because at high tem-
peratures (due to convection) this element is reduced to helium [11].

– Very slim but intense appears here the H-Balmer series, with the excep-
tion of Hα, as well as the D1,2 sodium absorptions at about λ 5900.