On the night of Aug 05/06, 2020, under good conditions, I acquired images of the star ASASSN-20jl, to check on its brightness. My measurements show that the star was fainter than it had been on UT Aug 01, but reveal no interesting behavior. Sigh.
I also acquired images of Ross 248 and GX And for our continuing study of their parallax and proper motion.
You can find some basic information on this star at the ASAS-SN Transients page.
The main setup was:
Notes from the night:
The object is at
RA = 16:46:14.62 Dec = +17:00:17.4 (J2000)
A chart of the field is shown below. The size of the chart is about 19 x 14 arcminutes.
I've marked the location of several comparison stars.
star ID B V ------------------------------------------------------------------------- A BD+17 3086 10.82 10.33 B TYC 1524-1170-1 11.64 10.45 --------------------------------------------------------------------------
I took a photo of the finder TV's screen when pointing to ASASSN-20jl; this could be a useful reference for the future:
I ran the camera at -19 Celsius. Nothing out of the ordinary.
I took a series of 53, then a subsequent 91, exposures of the field (separated by a gap when MaximDL froze), using the R-band filter and an exposure time of 20 seconds. The signal-to-noise of the target is still considerably lower than I'd like, but that's in part due to its fading.
The sky value shows that the sky was mostly clear, with a small bump due to some light cloud.
The number of objects detected.
I used an aperture with radius 5.0 pixels tonight for these measurements, due to the large FWHM.
Using aperture photometry with a radius of 5 pixels (binned 2x2, each pixel is 1.25 arcsec, so a radius of 6.25 arcsec), I measured the instrumental magnitudes of a number of reference stars and the target. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.
Sigma-vs-mag plots show that the floor was about 0.007 mag overall, which is better than it was the previous night on this target.
Here are light curves of the variable and the field stars.
I used the APASS value for the r-band magnitude of star "C" to shift the ensemble magnitudes to the standard r-band scale.
The variable has probably decreased in brightness in the past five nights: it measured V = 13.1 on UT Aug 01, and r = 13.9 on UT Aug 06. It showed no short-term variations during my measurements, so I'm giving up on this star.
This is one of the stars that a capstone student may study over the next year in a project involving parallax. Ross 248 is a relatively faint red star surrounded by many other stars of similar brightness, so it's a good candidate for high-precision parallax measurements.
These observations involved:
The object is (currently) near position
RA = 23:41:55.27 Dec = +44:10:06.38 (J2000)
A chart of the field is shown below. The size of the chart is about 41 x 27 arcminutes. The noisy area at right (West) is the shadow of the guider's pickoff mirror.
I've marked the location of several comparison stars.
star UCAC4 B V r ------------------------------------------------------------------------- A UCAC4 671-120730 12.617 10.689 B UCAC4 671-120688 C UCAC4 671-120749 10.987 10.663 P kappa And 4.06 4.14 --------------------------------------------------------------------------
I took a photo of the finder TV's screen when pointing to Ross 248; this could be a useful reference for the future:
I took a series of 50 exposures of the field, using the R-band filter and an exposure time of 20 seconds.
Using the same techniques as described for earlier nights, I matched detected stellar positions to the Gaia DR2 catalog; as usual, I used a linear model and included all stars in the catalog.
I am continuing to use the box
cr=650 sc=1000 nr=1300 nc=1000mentioned in the entry for Jun 28, 2020 to avoid vignetting and coma.
This is my eleventh measurement of Ross 248. The small hints of motion, negative in both directions, are consistent with the expected path of the object.
The dispersion of the derived positions continues to be smaller than it was earlier in the summer. Good.
Like Ross 248, GX And is a nearby (binary) star which will be the target of a parallax project in the coming year. One of the two components is bright -- about mag V = 8 -- so one must use short exposures to prevent it from saturating the detector. That may mean that this system isn't as easy to measure as Ross 248 or some others.
The object is currently close to this position:
RA = 00:18:28.4 Dec = +44:01:31 (J2000)
but it does have a very high proper motion.
A chart of the field is shown below. The size of the chart is about 41 x 27 arcminutes. The noisy area at right (West) is the shadow of the guider's pickoff mirror.
The two components of the GX And binary sit inside the box. I've marked the location of several comparison stars as well.
star UCAC4 B V r ----------------------------------------------------------- A 671-001473 9.939 9.790 B 670-001639 9.413 8.472 C 671-001509 12.712 11.421 11.001 -----------------------------------------------------------
I took a photo of the finder TV's screen when pointing to GX And; this could be a useful reference for the future:
Before I started making measurements of GX And, I re-focused the telescope. The best position was pretty much the same as it had been earlier: 0.640 (vs. 0.642 earlier). It was hard to find the best focus position: there wasn't much change in FWHM as I moved the focuser back and forth near the best value. Rats.
I took two series of 50 exposures of the field, using the R-band filter and an exposure time of only 5 seconds.
Using the same techniques as described for earlier nights, I matched detected stellar positions to the Gaia DR2 catalog.
The target is clearly moving in the positive RA direction, as we would expect from its known (large) proper motion.
Last modified 8/06/2020 by MWR.