by Ann » Thu Sep 27, 2012 12:56 am
Yes, the star HD 53367, the ionizing source of emission nebula Sharpless 2-292, is indeed classified as a Be star by the link given to us in bystander's post. My software, on the other hand, classifies it as a B0IV:e star. But there is something fishy with both classifications.
The author of the ESO post quoted by bystander wrote (or quoted another source):
HD 53367 is a young star with twenty times the mass of our Sun. It is classified as a Be star, which are a type of B star with prominent hydrogen emission lines in its spectrum. This star has a five solar mass companion in a highly elliptical orbit.
A star whose mass is twenty times the mass of the Sun is going to become an O-type star. Professor Jim Kaler wrote about 10 Lacertae, a well-known and very young star of spectral type O9V:
From a surface heated to a quite-amazing 32,000 Kelvin, it radiates a with a luminosity of 26,800 Suns (the majority of the light in the invisible ultraviolet), from which we derive a radius 4.7 times that of the Sun and a great mass of 16 times solar.
As for HD 53367, we may not that it is quite heavily reddened. We can actually see a thick black dust lane snaking in front of the star, except that it appears to have been cleared away just where it passes the star. But obviously there is still a lot of dust between us and the star deflecting away much of its light. Indeed the apparent color and brightness of this intrinsically bright blue star shows it to have lost a lot of light due to the surrounding dust. The star's B-V index is +0.36, which is far more appropriate for an F-type star than for one of spectral class B. Its luminosity, as derived from its apparent brightness and its distance from us calculated from parallax, is 88 times the luminosity of the Sun. That's ridiculously low for a hot young star surrounded by a significant emission nebula.
Has this star already run through its main sequence lifetime and evolved into a larger but cooler star of spectral class B? I find that unlikely. There are other blue stars in the Seagull Nebula which are classified as B0IV stars, but they are not surrounded by such obvious emission nebulae, and therefore they don't appear to be equally young. The shape of the Seagull suggests to me that star formation is running from the left part of the picture to the right part of it. Admittedly the bright "ridge" running along the length of the Seagull nebula suggests that star formation may be going on on both sides of it, blowing remaining gas into a ridge. But if it is true that star formation on the right side of the ridge has started later than the star formation on the left of it, then HD 53367 ought to be one of the youngest of the bright blue stars here. But if it is so massive and so young, why isn't it an O-type star?
Ann
Yes, the star HD 53367, the ionizing source of emission nebula Sharpless 2-292, is indeed classified as a Be star by the link given to us in bystander's post. My software, on the other hand, classifies it as a B0IV:e star. But there is something fishy with both classifications.
The author of the ESO post quoted by bystander wrote (or quoted another source):
[quote]HD 53367 is a young star with [b][i][color=#0040FF]twenty times the mass of our Sun[/color][/i][/b]. It is classified as a Be star, which are a type of B star with prominent hydrogen emission lines in its spectrum. This star has a five solar mass companion in a highly elliptical orbit.[/quote]
A star whose mass is twenty times the mass of the Sun is going to become an O-type star. Professor Jim Kaler wrote about 10 Lacertae, a well-known and very young star of spectral type O9V:
[quote]From a surface heated to a quite-amazing 32,000 Kelvin, it radiates a with a luminosity of 26,800 Suns (the majority of the light in the invisible ultraviolet), from which we derive a radius 4.7 times that of the Sun and a great mass of [b][i][color=#0040FF]16 times solar[/color][/i][/b].[/quote]
As for HD 53367, we may not that it is quite heavily reddened. We can actually see a thick black dust lane snaking in front of the star, except that it appears to have been cleared away just where it passes the star. But obviously there is still a lot of dust between us and the star deflecting away much of its light. Indeed the apparent color and brightness of this intrinsically bright blue star shows it to have lost a lot of light due to the surrounding dust. The star's B-V index is +0.36, which is far more appropriate for an F-type star than for one of spectral class B. Its luminosity, as derived from its apparent brightness and its distance from us calculated from parallax, is 88 times the luminosity of the Sun. That's ridiculously low for a hot young star surrounded by a significant emission nebula.
Has this star already run through its main sequence lifetime and evolved into a larger but cooler star of spectral class B? I find that unlikely. There are other blue stars in the Seagull Nebula which are classified as B0IV stars, but they are not surrounded by such obvious emission nebulae, and therefore they don't appear to be equally young. The shape of the Seagull suggests to me that star formation is running from the left part of the picture to the right part of it. Admittedly the bright "ridge" running along the length of the Seagull nebula suggests that star formation may be going on on both sides of it, blowing remaining gas into a ridge. But if it is true that star formation on the right side of the ridge has started later than the star formation on the left of it, then HD 53367 ought to be one of the youngest of the bright blue stars here. But if it is so massive and so young, why isn't it an O-type star?
Ann