Saturday, February 06, 2021

another double query

So, Chris B asked about another double...

He thought it was a Herschel, written as a number followed two H's, a capital then a lower case, italicised, and then another number as:

41 (Hh 753)

I had never seen something like this. I did some digging. A tricky one....

Google referred me to a book. Memoirs, Volume 40 (XL), by the Royal Astronomical Society. It appears to be a complete catalogue publication with 10,300 doubles.

Viewed the big table called:

Sir John Herschel's Catalogue of Approximate R.A.'s and N.P.D.'s of Double Stars.

On page 121, I found...

  • Entry 9457
  • Hh 753
  • aka 41 Aquarii (with a dagger)
  • RA 22 4 54 (h m s)
  • NPD 111 55 (° ')
  • data from 1830

I didn't know what NPD was. The amazing wikipedia to the rescue:

In some 18th and 19th century astronomical texts, declination is given as North Pole Distance (N.P.D.), which is equivalent to 90 – (declination).

That meant NPD 111 55 is -21 55 Dec.

When I looked up 41 in SkyTools, I noted:

  • R.A.: 22h14m18.1s
  • Dec.: -21°04'27"
  • aka H N 56, HR 8480, HD 210960, SAO 190986, PPM 273536, and HIP 109786.
  • AB: 5.33+7.16 mag
  • PA 112°
  • Sep 5.10"

The RA and Dec from the old book didn't seem to match 41 Aqr. There was nothing notable, no obvious double, at the "old" location. And 41 Aqr was over 2 degrees away.

Checked Stelle Doppie for 41 Aqr. Nothing in the notes...

Is it 41 Aqr after significant proper motion? I don't know how to assess that. But 2 degrees seems like too much in 200 years.

I read the preamble in the Memoirs. I believe the Hh 999 convention refers specifically to John's father's (i.e. William) catalogue. I learned the dagger (or obelisk) mark indicated the item was documented and validated in other document or manuscripts.

It was all a little inconclusive.

I asked Chris for other data. Magnitudes, PA, Sep?

He replied a short while later, "Yeah I think it must be 41 [Aqr], Webb lists them as 6 & 8th Magnitude and ~11.2" separation."

I pointed out it couldn't be 41. The mags and separation didn't match.

In the meantime, I ran a search in Stellarium. Looked for doubles in a 5 degree circle in the area. Nothing matched Chris's numbers... Bogus binary? Dubious double?

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