TV Cas
Posted: Sat Nov 06, 2021 12:39 pm
Hello.
TV Cas is an Algol type eclipsing binary composed of a bright B9V star and a F7IV companion. The bright star, according to the article by K.Walter(1979), makes the F7IV very difficult to distinguish. It has a 1.81 days' period.
Threre was a predicted minimum at the beggining of the night of September, the 29th. Althought i have many years experience in photometry, i only started doing spectroscopy about a year ago. I have obtained many spectrums of different types so far and i wanted to try my luck in detecting variability in a binary.
So i started obtaining Mile's HD3360 B2V star spectrum to be used as instrumental response and then continued obtaining TV Cas 180 seg spectrums and then left the observatory unattended for the rest of the night. Autoguiding went well and i got 150 spectrums. I stacked then in groups of fifteen using Demetra and finnally got 10 spectrums. I processed them twice. Once without using instrumental response and another using it.
I also obtained many images using the finder to measure TV Cas photometry. Next figure shows the resulting curve, just as predicted for the minimum.
According to Walker's Spectroscopy Atlas, F type stars have as charasteristics a decreasing Balmer lines intensity, but increasing Mg triplet (5168-83) and CH band(4300).
So i measured, using the spectrums without the instrumental response, EW at Hgamma and Mg. To achieve it, i cropped the spectrums to the area around the absotion line, eliminated the continuum and normalized all of them so that the intensity value was one in the flat part out of the absortion line. Then i measured EW in each spectrum carefully trying to use the same limits at the figure. For this analysis i used BASS software.
I obtained this curve for H gamma. As expected, as the bright star brightness is less and the F star spectrum may show up, Hgamma intensity is minimum coincidental with photometry minimum. Then again, i consider that measuring EW correctly is difficult and my result could be just a coincidence. Maybe the air mass is to blame?
I would love to hear comments on this.
On the other hand, i also measured the Mg triplet EW and obtained just the opposite curve, that is, maximum EW at the minimum in the photometry curve, also as expected.
Also, i had a look at the spectrums in which i used the instrumental response. The star used for this response was acquired only once, at the beggining of the session. It was close to TV Cas.
In it it is clearly shown the CH band at 4300 Angstron in the spectrum at minimum brightness and its ausence in the spectrum at maximum brightness.
I also added up in BASS the two B and F type synthetic spectrums to check the result, and it seems very similar to what i obtained at minimum brightness.
As a summary, i think i could observe that mimimum in the spectrums. But i am just starting in this spectroscopy world and i am not sure if the procedures i used are correct.
Specially in the EW measurement and the use of a star as instrumental response only once.
Any advice would be very welcome.
Equipment used for the spectrums:
-Meade 12"LX200 with an Optec reducer, making it f/5.5
-Atik 460 EX camera
-LISA spectroscope
Equipment used for photometry:
-EVOGuide 50 telescope
-Atik Titan camera
TV Cas is an Algol type eclipsing binary composed of a bright B9V star and a F7IV companion. The bright star, according to the article by K.Walter(1979), makes the F7IV very difficult to distinguish. It has a 1.81 days' period.
Threre was a predicted minimum at the beggining of the night of September, the 29th. Althought i have many years experience in photometry, i only started doing spectroscopy about a year ago. I have obtained many spectrums of different types so far and i wanted to try my luck in detecting variability in a binary.
So i started obtaining Mile's HD3360 B2V star spectrum to be used as instrumental response and then continued obtaining TV Cas 180 seg spectrums and then left the observatory unattended for the rest of the night. Autoguiding went well and i got 150 spectrums. I stacked then in groups of fifteen using Demetra and finnally got 10 spectrums. I processed them twice. Once without using instrumental response and another using it.
I also obtained many images using the finder to measure TV Cas photometry. Next figure shows the resulting curve, just as predicted for the minimum.
According to Walker's Spectroscopy Atlas, F type stars have as charasteristics a decreasing Balmer lines intensity, but increasing Mg triplet (5168-83) and CH band(4300).
So i measured, using the spectrums without the instrumental response, EW at Hgamma and Mg. To achieve it, i cropped the spectrums to the area around the absotion line, eliminated the continuum and normalized all of them so that the intensity value was one in the flat part out of the absortion line. Then i measured EW in each spectrum carefully trying to use the same limits at the figure. For this analysis i used BASS software.
I obtained this curve for H gamma. As expected, as the bright star brightness is less and the F star spectrum may show up, Hgamma intensity is minimum coincidental with photometry minimum. Then again, i consider that measuring EW correctly is difficult and my result could be just a coincidence. Maybe the air mass is to blame?
I would love to hear comments on this.
On the other hand, i also measured the Mg triplet EW and obtained just the opposite curve, that is, maximum EW at the minimum in the photometry curve, also as expected.
Also, i had a look at the spectrums in which i used the instrumental response. The star used for this response was acquired only once, at the beggining of the session. It was close to TV Cas.
In it it is clearly shown the CH band at 4300 Angstron in the spectrum at minimum brightness and its ausence in the spectrum at maximum brightness.
I also added up in BASS the two B and F type synthetic spectrums to check the result, and it seems very similar to what i obtained at minimum brightness.
As a summary, i think i could observe that mimimum in the spectrums. But i am just starting in this spectroscopy world and i am not sure if the procedures i used are correct.
Specially in the EW measurement and the use of a star as instrumental response only once.
Any advice would be very welcome.
Equipment used for the spectrums:
-Meade 12"LX200 with an Optec reducer, making it f/5.5
-Atik 460 EX camera
-LISA spectroscope
Equipment used for photometry:
-EVOGuide 50 telescope
-Atik Titan camera