Phi Andromeda

[Keith Graham]

Hi,

I wonder if someone can help me tp understand the spectral changes in Phi And. There is an Ha emission line profile embedded within the Ha absorption profile. Over time, the emission line appears to shift left and right and is sometimes dead center of the absorption line. I have even seen a spectrum with no emission line.

I have found that this star is a binary system. The primary is a B7Ve star with V mag = 4.46. The companion is a B9V star with V mag = 6.06.

At first I thought the emission line shift could be due to the revolution of the companion around the primary, but the orbital period is approx. 554 years. Besides, it is the primary that is the Be star, so the primary’s disc must be the source of the emission line. I would suspect that the reason for the occasional disappearance of the emission line would be the dissipation of the disc. When a new disc “erupts” the emission line would then reappear.

So my questions:

1) Most of the Be spectra I see have an emission line with an absorption line within it. The depth of the absorption line is determined by the inclination of the star/disc to our line of sight. So why is there an emission line within an absorption profile inn Phi And, which is just the reverse of what we normally see.?
2) What causes the shift in that emission line?

I tried uploading 2 of my spectra as examples of what I am talking about ,but I get the messages that fit and dat extensions are not allowed.

Cheers,

Keith Graham

[Robin Leadbeater]

Hi Keith,

You can upload any file type as long as you zip it first.

Cheers
Robin

[Robin Leadbeater]

Hi Keith,

I have had a look at some phi And spectra in BeSS. I think what we are seeing is the emission line superimposed on the normal B star photospheric absorption line. The emission line does seem extremely narrow, compared with gam Cas for example. Perhaps we are viewing the star exactly pole on so there is no Doppler broadening due to rotation of the disc.

Cheers
Robin

[Robin Leadbeater]

Perhaps we are viewing the star exactly pole on so there is no Doppler broadening due to rotation of the disc.

That would not explain how the emission line could move relative to the absorption line though

Robin

[Keith Graham]

Hi Robin,

Yes, it is that shift that has peaked my curiosity.

What also impressed me was the extreme width and depth of the absorption profile. Many of the BeSS stars I have been observing have a pretty level continuum up to the emission profile. I am also confused as to why the emission profile would shift but not the absorption profile. I am sure there is a logical explanation for all of this, but being a beginner in spectrum interpretation, I need some guidance from those who have done this for awhile. BTW- I also noticed that one of the spectra in the BeSS DB showed absolutely no emission line - just the absorption line. So apparently that disc comes and goes:).

Oh yes- thanks for the tip on uploading images.

Cheers,

Keith

[Robin Leadbeater]

BTW- I also noticed that one of the spectra in the BeSS DB showed absolutely no emission line - just the absorption line. So apparently that disc comes and goes:).

Oh yes, that's a characteristic of Be stars and still not well explained. Valerie's summaries of BeSS data show several such activity changes
http://www.astrosurf.com/aras/surveys/beactu/index.htm

I think whether the absorption wings remain visible depends on the shape and strength of the emission component.

Robin

[Keith Graham]

Hi Robin,

>I think whether the absorption wings remain visible depends on the shape and strength of the emission component.

AH HA! So if the emission component is strong, would that "overpower" the absorption component as to make it virtually invisible? And a weaker emission component allows the absorption wings to be more visible? If I have that correct, that would make perfect sense to me and be a major step forward in my understanding the various spectra.

Cheers,

Keith

[Keith Graham]

Hi Robin,

I have not received any replies to my observations to my question in the previous post on this topic, so I will try again.

I am trying to get a handle on what is happening with Phi And in my quest to understand and interpret stellar spectra.

Robin mentioned:

"I think whether the absorption wings remain visible depends on the shape and strength of the emission component."

My question was:

"So if the emission component is strong, would that "overpower" the absorption component as to make it virtually invisible? And a weaker emission component allows the absorption wings to be more visible? "

Could someone please verify if my thinking is correct or where it might need tweaking?

I do notice that some spectra show only an emission component with no absorption component, but I would think there should be an absorption component somewhere in that spectrum. Is there anyway where the absorption component could be absent other than being "overpowered" by the emission component?


Thanks a bunch,

Keith Graham