Affiliation
American Association of Variable Star Observers (AAVSO)
Tue, 07/26/2022 - 23:46

Hi all. I am just getting started in photometry and have been looking for a program to start. So I was checking out the alerts and alert 786 seems like something I can do and would like to try. Now I have a few questions regarding the alert. The alrert states. 

"The preferred cadence of observations would be to image the star with a spacing of 1-3 minutes (maximum of 5 minutes) between exposures for as long as the star is visible each night, for several continuous nights. Gaps of roughly 10 days to 2 weeks between 3 (+/-) nights of observations over the course of 2 or 3 months should allow us to fully characterize the overall changes."

Could someone help me understand the Cadence in terms of calculating the magnitudes. Am I to median stack all of the subs I get during the night and then do photometry? Or do I do photometry on the each image and sumbit an average of the results?  Or something else?  

My last question is although they're requesting V band observations does that mean I do not need transformations or I should still transform and get a transformed magnitude. 

 

cadence

Hi,

I'll let the more experienced photometry observers guide you into a program. Me, I started with LPVs and am still enjoying gathering data on them. Cadence however is a reference to the time lag between photometric measures. In the alert the desire is to know the magnitude of the star every 1 to 3 minutes (no more than 5 minutes apart).

Clear Skies!

JENJ

Affiliation
American Association of Variable Star Observers (AAVSO)
Hi Alfredo,First, Alert…

Hi Alfredo,

First, Alert 786 concerns an RR Lyrae star, V0338 BOO.
By going to the VSX (https://www.aavso.org/vsx/index.php?view=detail.top&oid=146816) we notice that its variation is almost half a day (0.494047 d (11.8571 h )).

In photometry, we apply to have the target having a signal min. of 100 SNR (Signal Noise Ratio), the exposure time is important for the star not being overexposed, nor underexposed. Software like MaximDL displays this base value. Thereafter, it is necessary to accumulate the images. Here the V filter is recommended.
But normaly, we can use B, V, R I. These filters "cut" specific bands in frequencies of the visible spectrum.

Subsequently, the images are processed by Dark, Bias and Flats, like astrophotography, before doing photometry in order to measure the brightness of the target, compared to other stars which serve as a reference or "check stars", such as it is well explained in the alert. Several software can be used for processing and photometric measurements. It's a question of choice. MaximDL (paid software), AIP4Win (now free), Muniwin, Lesvephotométrie... There are several.
My personal choices go to the first two.
Then we make a report in AAVSO format and send it to AAVSO (https://www.aavso.org/databases).

What must be remembered is that each image constitutes a measurement and that the photometric precision depends on the correct exposure time which offers the best SNR of the images, then of the number of images, because the atmosphere will always affected our images somewhat, it's the law of averages.

For more information, you can consult the photometry manual (https://www.aavso.org/observing-manuals) and of course, there are the photometry courses.

Hoping to have met expectations,

JBD