On the night of Aug 19/20, 2019, through hazy, moon-lit skies, Evan Muskopf and I acquired a set of observations of the likely black-hole system MAXIJ1820+070, (also known as ASASSN-18ey ). It remains in a bright, flickering state at a magnitude of approx V = 14.1.
In addition, we set up and observed for the first time through a classic 1960s Unitron refractor which had been donated to the Observatory by a former RIT Physics professor. It provided some sweet images!
One of our former RIT Physics faculty members, John Shaw, graciously donated a vintage Unitron 105mm refractor to the Observatory. Since it had been sitting in a box for several decades in a slightly damp area, it had accumulated a bit of fungus on the lenses, and some rust here and there. I spent some time cleaning it up, and was ready to try looking through it for the first time tonight.
Evan Muskopf helped me to move it onto the sidewalk and parking lot, so we could have a good view of Saturn and the Moon. We managed to find a proper focus, and were mighty impressed. Evan attached his cellphone to the scope using an adapter and took some pictures via eyepiece projection. These are our first attempts, taken when the Moon was only about 20 degrees above the horizon, but they surely show a lot of detail.
This optical and X-ray and radio transient is likely a black hole accreting material at a higher-than-usual rate. It has been the subject of many observers over the past few months -- see the trail of telegrams that include
The main setup was:
Notes from the night:
No problems with hardware or software tonight.
The object is located at
RA = 18:20:21.9 Dec = +07:11:07.3
A chart of the field is shown below. The size of the chart is about 22 by 18 arcminutes.
I've marked the location of several comparison stars, which also appear in light curves below. Stars C, D, and E are mentioned by the Tomoe Gozen team in ATel 11426, but all three are rather red, with (B-V) ranging from 1.14 to 1.37. Star B is one of the bluest nearby bright stars, with (B-V) = 0.52.
star UCAC4 B V ---------------------------------------------------- B 486-079513 12.975 12.454 C 486-079608 13.968 12.830 D 486-079523 14.637 13.272 E 487-077858 14.637 13.272 ----------------------------------------------------
I ran the camera at -17 C. Nothing out of the ordinary.
The sky value shows only a very brief period of thin clouds.
Here's a record of the telescope's drift. For the most part, it tracked well with 5-second exposures; I've increased the X aggressiveness from 0.1 -> 0.5.
The number of objects detected -- I required 100 objects for an image to be included in the ensemble.
I used an aperture with radius 4.0 pixels. No changes in focus position during the run.
I discarded images which had obvious trailed stellar images, and also images which were outliers in the "image adjustment" plot. (discarded a total of 56 of the 322 raw images).
Using aperture photometry with a radius of 4 pixels (binned 2x2, each pixel is 1.34 arcsec, so a radius of 5.4 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 0.009 mag overall. I did NOT mark star "A" as variable in the ensemble. MAXI is the outlier at ensemble mag of about 3.4.
Here are light curves of the variable and the field stars.
I used the UCAC value for the V-band magnitude of star "B" = UCAC4 486-079513 to shift the ensemble magnitudes to the standard V-band scale.
Here's a closeup on the variable.
You can download my measurements below. A copy of the header of the file is shown to explain the format.
# Measurements of MAXIJ1820+070 made at RIT Obs, UT 2019 Aug 20, # in good conditions, # by Evan Muskopf and Michael Richmond, # using Meade 12-inch LX200 and ATIK 11000. # Exposures 30 seconds long, clear filter. # Tabulated times are midexposure (FITS header time - half exposure length) # and accurate only to +/- 1 second (??). # 'mag' is a differential magnitude based on ensemble photometry # using a circular aperture of radius 4 pix = 5.3 arcseconds. # which has been shifted so UCAC4 486-079513 has mag=12.454 # which is its V-band magnitude according to UCAC4. # # UT_day JD HJD mag uncert Aug20.06558 2458715.56558 2458715.56877 14.047 0.021 Aug20.06608 2458715.56608 2458715.56927 14.127 0.020 Aug20.06659 2458715.56659 2458715.56978 14.024 0.021
Last modified 8/20/2019 by MWR.