Hello everybody!
I am right now reducing some spectra captured last night. In order to produce the spectrum of zet Gem, I used as a reference star HD 56537, better known as lam Gem.
It turns out that this is a high proper motion star, that shows very clearly H-alpha emission.
However, in the literature (Simbad, AAVSO, Britastro, and Gaia DR3) either classifies this star as A4IV or no data is available whatsoever.
Found it interesting to show this to you.
Cheers!
Enrique Boeneker
(BETB)
Hi Enrique,
I think you have found something new about this star.
I have searched a little bit in the literature, and I found some measurements of Hydrogen lines of this star by Stock and Bappu in 1955 and 1962, but they were not considering Halpha.
Later in 1980 Mermillion measured the equivalent width of Halpha founding it in absorption, and in 1985 Burnashev performed spectrophotometry and found also absorption.
I searched also on the ESO archive, and it was observed 40 times from 2006 to 2011, and the reduced spectra shows always absorption (on the link below go over the magnifying glass to see the preview of the spectra).
From Gaia DR3, there is a companion with the same proper motions at 8 arcsec (that gives approx 245 AU of projected separation) and 6 magnitudes fainter that roughly point to a K2V star. It is very difficult that this star could have contributed to the Halpha emission in the way is visible in your spectra.
Below there are the links of these data.
Congratulations!
cheers
m
Mhhhh! Interesting!
Thanks for your interest! Well, lets take this first with a pinch of salt, and let me go through the literature you found. Let me repeat today (weather allowing) another capture of the spectrum of this star and see if I get this emission again. I also will do some photometry in all the filters (although the interesting ones would be R_c and I_c. So lets see what comes out.
Thanks again for your comment and links!
Cheers!
Enrique
(BETB)
I forgot to check TESS, but here we are. As expected, this is a short period pulsator with amplitude approx 1 millimag and 0.6 day period.
Hey again!
I took a fresh spectrum of lam Gem yesterday. The “emission” line is still present, if it is indeed an emission line, of course.
I have some doubts about it now. Taking a closer look at my yesterday’s spectrum, and since it is very low res, you could infer:
So, what I will do tonight is to change the angle of my camera a bit and see what happens. This in order to discard or confirm point number 4.
This is fun!
Cheers!
Enrique
(BETB)
Hi Enrique, 2 angstroms are not so much they correspond to roughly -90 km/s. On the other side the shape of the line on the wings looks very similar to emission lines, and seems asymmetrical. The weird part is that the negative value point to a receding object. The star is also receding but at only -15 km/s.
Cheers m
Sorry Enrique, i made a mistake in the previous message.
The -90 km/s is pointing toward something that is emitted by star toward us, 75 km/s faster than the star. Maybe is a bubble of gas emitted by the star, a sort of big coronal emission.
Remember, Mauro, that this is a low res spectrum. We cannot determine radial velocity due to the intrinsic nature of this kind of spectrum.
I really appreciate your interest! Let me do that “last”-previous test, only to be 100% sure that this star is emitting light at that approximate wavelength.
Cheers!
Enrique
(BETB)
A high resolution R~15000 spectrum of lam Gem tonight shows no H alpha emission.
The absorption profile is consistent with the A3/4 IV/V classification
Cheers
Robin
Do you have an image of the field to confirm you have the correct star ?
Robin
Also the “emission” is very narrow. Much narrower than the apparent resolution of the spectrum based on the other Balmer lines so it is unlikely to be real (a cosmic ray hit or hot pixel ?) what spectrograph is this ? Have you checked the raw image ?
Cheers
Robin
Hello, Robin.
Thanks for joining in! Here’s an image of the actual data I am processing (one raw frame of 30 s):
I’m using the SA100 paired with an ASI178MM and an Askar FRA500 (90 mm/500 mm) refractor. The distance between the grating and sensor is of about 40 mm if I remember well.
I discard a cosmic ray, because it is pretty unlikely that such a thing will hit my sensor repeatedly during two nights at exactly the same spot. Your guess of a hot pixel is also unlikely, since the images of the two nights are offset from one another.
On the other hand, I have been using plate solving to fix the object in the frame (with a tolerance < 3.5 arcminutes), so I do not believe that I have been observing a different star.
I would put my money now on the small intruding star hypothesis. When I repeat the observation tonight, I will slightly rotate my camera. I am almost certain that the absorption line will appear again.
Cheers!
Enrique
(BETB)
Hi Enrique,
Yes, plate solving your image, I can see the “emission” is the mag 9 star BSD 75-2173 which
landed exactly in the spectrum
Cheers
Robin
The forum mangled the link, perhaps this will work
Cheers
Robin
Thanks, Robin.
I won the bet then! Hahaha.
Cheers!
Enrique
(BETB)
Hey everybody!
Just to give this thing a closure. Here’s my yesterday’s spectrum of lam Gem.
No H-alpha emission line. What did I do? Just rotate the camera some degrees and that was it. As @Robin_Leadbeater confirmed yesterday, a low magnitude star was causing the “H-alpha emission line”. My question is, what are the chances for this? Should I run to buy a lottery ticket? 
Cheers!
Enrique
(BETB)
Hello Enrique,
I know this was already solved, but I only just now saw this thread. By coincidence I captured a spectrum of lam Gem on March 28. It was my reference star for the session. Here’s the spectrum:
Captured with a Lowspec 3.0 on a C8.
Regards,
Johannes
Niiiiice spectrum!!!
