Sat, 09/07/2013 - 14:07
Hi,
Been monitoring HT-Cas star several nights ( 12"F4 + Starlight MX716 ccd + Baader IRcut 90sek exp.) When making measures, i,d take star 172 (AAVSO Chart 12645FMI ), as chek star to see how accurate my measures is in low SNR. Seems to mee that star 172 is varying slightly. I compared star 172 to as bright star USNO-A 1500-01193693 (Chk 3) and it show no trace of such wobbling.
I'm right or is it my error?
I'm not see my attachment, I thought I'd put.
Attachment again..
EDIT: just notised, in pic, blue line is Chk1 star (160) Not Ref1 (152) - marked wrongly!
I remeasured (essemble, four refstar) eight night obs, and double chekked them. Put all best measures - 1536 total - in Peranso, and it gave a "lightcurve" of refstar 172. Amplitude is 0.05 mag and 3.78h perioid.
I'm not a pro with Peranso , and I am not sure that I got the right result.
Result in attachment - screenshot.
It would be nice if someone could confirm the observation :)
Hi, Timo,
The light curve looks like a typical DSCT light curve, the right shape and amplitude and the right period (0.1577 d.).
I don't see any mention to the passband in your postings or in the plot. Are you using a V filter or just working unfiltered and using Vmags. of your comp stars for calibration?
Just trying to explain why your magnitudes (17.01-17.08) are 0.15 mag. or so brighter than the V values published.
The star's colors are redder than normal for DSCT (B-V= 1.00; V-I= 1.36; J-K= 0.59) but the extinction in this area could be ver large [E(B-V)= 0.7] so that shouldn't be a problem.
It would be good to see if someone else can reproduce your variability but I think this is very likely a DSCT.
You should submit it to VSX.
Read the submission guidelines:
http://www.aavso.org/vsx/index.php?view=about.notice
and use the New Star Wizard to submit it. The phase plot you attached is okay for your submission.
Give the period in hours and find the star's position in UCAC4 and other identifiers through VizieR to make your submission complete.
Cheers,
Sebastian
Thanks Jim and Sebastian for replying!
First A little background information about me:
I write in English using google translator. I'm a regular plumber jack, and not capable to do "hard science" Just monitoring variables because they are very interesting creatures. By-product on my hobby is lightcurves, i share on AAVSO database, and they may be useful for real scientists - sometime in the future. My intention is to get the accurate measurements - short term variation - within hardware capabilities and my skills.
Then the business :
My first post, the first line: "(12"F4 + Starlight MX716 ccd + Baader IRcut 90sek exp.)" I,d try tell that I was using 12"F4 telescope, StarlightMX716ccd camera, Baader IRcut filter and 90sek shutter speed. Working as unfiltered and using V-mags (even though was using tahat Baader IRcut filter (as a dust cover)) Last 3 nights 5-8. 9. i used 75sek shutter speed ,the moon disappeared from interfering.
I do the measurements whit Maxim DL4 software, I have not figured how to make error bars. Just found FotoDif software, which do errorbars (attatchment), not knowing how make AAVSO report whit FotoDif.
Four refstars, wich I used to measure Ref172 for Peranso analysis - see attatchment. Look star 159 is more dimmer in my pic than star 160. So I know my absolute magnitudes are not right, my point is posibble variability of reference star. In conditions pic - Drift xy pix - are not real, I kalibrate and aling all pics before measure them.
And : http://www.aavso.org/vsx/index.php?view=about.notice
It takes a week, to me understand those instructions - way too much English!
Timo kindly send me his data for a second look but as we've already seen the result was beyond doubt. The original data were resampled to give approximately the same weight to each point and run through a Lomb-Scargle periodogram. The result is the same as before P1=0.15772(4) but with this removed there is a suggestion of low-level variation at higher frequencies. I have done a two-period Fourier fit with P2=0.10610(5) but this is only a suggestion as the full amplitude is 0.02 magnitudes and shows the upper limit of any secondary variation. Delta Scuti stars are often multi-periodic so other periods would not be a surprise.
Power_1 - Lomb-Scargle periodogram of resampled data
Power_2 - ... with P1 removed
Phase2 - Two-period Fourier fit
KTU
I''m probably not the best person to answer this but no one else seems to be stepping up so...
I don't know what telescope or camera you are using or what your sky conditions are but your error may well be over 0.06 at 17.2. I checked your observations of HT Cas to get a ball park on your error but you don't provide an error so that doesn't help. So just based on your observations it would be hard for me to conclude that 172 is variable.
If I were you I would first try to get a handle on the error of my HT Cas observations. That will give you some idea of how much faith to put in the 0.06 variability at 17.2
If I check VizieR, I see no evidence that it is variable. Comp 172 is from Henden USNO 1 meter and has a stated error of 0.02. The Henden comps are usually pretty solid.
But others are a lot better at this than I am, so you might be right.
Jim Jones
I did a quick analysis of the images of an older HT Cas run from 2010. Though the exposure time was too short for the 172 star it still shows the same variation Timo reported. So the star is a variable.
I am planning an observing run as soon the weather improves.
arto
The Henden NOFS 1.0m calibration photometry for this star was done on 3 nights in 1995. These BV exposures were 2minutes/1minute for B/V, in order to calibrate the bright end of the sequence. These exposures are short for a 17th magnitude star, so the 0.02mag quoted error is probably an underestimate, caused by small number statistics. Note that B has a higher error. Nonetheless, low amplitude variability is always difficult to see with only 3 snapshots, and there are undoubtedly other variables among those picked for comparison stars from my photometry, which is one of the reasons that we tend to avoid the blue stars when choosing a sequence. The light curves from Arto and Timo are pretty conclusive, and the amplitude falls within about one sigma of my average value.
As Sebastian indicates, delta Scuti variables are blue and this star has (B-V) = 1. This discrepancy is not unreasonable, considering that there is galactic extinction/reddening in this field. Congratulations to Timo on his discovery!
Arne
We did simultaneous observing runs of the new variable (and HT Cas of course). The light curves match very well showing the expected variation. My data points (OAR) have been shifted by 0.5 mags for clarity. Timo's (KTU) are in reference of the HT Cas sequence (V).
arto
Thank you very much to all who participated in this. particular, Arto, confirmed the findings.
I think it looks very much like a new variable :)
Now someone should get 172 out of the reference, and turn it into a variable?
There: http://www.aavso.org/vsx/index.php?view=about.notice
is too many parameters and too many steps to me to do job properly..
Cheers,
Timo
I have just submitted this star into VSX.
arto
I have removed the 172 star from the HT Cas sequence and edited its AUID record to "variable". Thank you for letting us know about this variable comp star.
Mike Simonsen
AAVSO Charts and Sequences Team
Thanks Arto for submitting it.
After a couple of editings it will be approved and visible to everybody.
Cheers,
Sebastian
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Sebastian Otero
VSX Team
American Association of Variable Star Observers