A spooky coincidence, or déjà vu all over again?

At the Fall 2000 Meeting, David Levy recounted Clyde Tombaugh’s discovery of a variable star on a pair of Lowell Observatory plates during the search for trans-Neptunian planets. David took an interest in this star, and when he checked it on the Harvard patrol plates, he found that it was a previously unrecognized dwarf nova (see David’s paper, “Tombaugh’s Star: A Historical Tale of the Cataclysmic Variable TV Corvi,” AAVSO Journal Vol. 28, p. 38).

After the Fall Meeting, I spent several days at Harvard College Observatory, tracking down lost or neglected variable stars. Tuesday was Halloween, and that evening the streets around Observatory Hill were swarming with little witches and goblins. I was working late every evening in the plate stacks, identifying variables discovered by W. J. Luyten during the Bruce Proper Motion Survey back in the early 1930s. (See my paper “Unfinished Business: Luyten’s Harvard Variables-I” in AAVSO Journal Vol. 28, p. 12.)

Luyten discovered nine variables on the pair of plates for Bruce Region 320 in Vela. I located his discovery marks on the plates, determined accurate positions of the indicated stars, and marked them on finding charts for the variable star catalogue team in Moscow. One of these “lost” variables was NSV 4834, originally Harvard Variable 8280. Luyten estimated it as 12.5 magnitude on one plate and invisible, fainter than 15.5, on the other plate.

In addition to identifying Luyten’s variables, another of my goals in this project is to investigate some of his brighter discoveries to determine variable types and periods. When I checked the vast Harvard plate collection, I was pleased to find more than 100 plates of this field taken with the 25-cm Metcalf astrograph.

All in all, 14 of Luyten’s discoveries can be observed on this set of plates, so I decided to make this field a special project. But my time in Cambridge was running out. Since I couldn’t observe all 14 variables on more than 100 plates in the time remaining, I decided to do the easy Mira variables and save the others for a later visit. I picked out five probable Miras based on their reported amplitudes of three magnitudes or more. One of these stars was NSV 4834.

After setting up comparison star sequences, I began to estimate the five selected variables on each plate. NSV 4834 was fainter than the plate limit on the first ten plates, which wasn’t surprising for a large-amplitude Mira. But it popped into view at 12.6 magnitude on the 11th plate.

Wait a minute! I had just recorded it as fainter than 14.6 on the previous plate, and that plate’s Julian Date was just three days earlier. This was no Mira. The next plate, 38 days later, showed the variable fainter than 15.8, but 15 days after that it was 13.4. Plates on the following two nights showed the variable dimming by 0.6 magnitude per night. By examining just 15 plates, I had found and confirmed a previously unrecognized dwarf nova (now V383 Vel).

Only five days after hearing David Levy tell how he had followed up on Clyde Tombaugh’s single observation of a variable star on a pair of plates and discovered a dwarf nova, I had followed up on W. J. Luyten’s single observation of a variable star on a pair of plates and discovered a dwarf nova. Both dwarf novae erupt to 12th magnitude and decline to around 17th. Both variables were originally discovered in the early 1930s, during searches for other types of objects, and then ignored, and both were eventually followed up by AAVSO members at the Harvard plate stacks.

All this is a pretty spooky coincidence. But the Harvard plate stacks can be a pretty spooky place late at night, when the long aisles of steel cabinets are silent and dark. Perhaps at the midnight hour, when moonlight shines through the tall windows, the plates whisper to each other about the secrets they still conceal-secrets waiting to be revealed to those who dare to seek them. Mwa-ha-ha-ha [Deep, sinister laugh].

Afterword: Okay, coincidences can only be stretched so far. I’d just like to point out that David Levy had to examine 10 Harvard plates before finding an outburst of TV Crv, while I had to look at 11 plates before finding an outburst of V383 Vel. Also, David’s last name is completely different from mine. So where’s the coincidence?

Table of contents