The Starry Night, 62

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9/07/2011. Tropical storm Lee and its remnants have put an end to deep-sky viewing for a few nights. I brought the telescope and mount inside and have been making some small repairs to the trailer, observing table, etc. Also thinking about how to improve the observing area where I have tromped the grass down to bare mud.

I'd like to get a photo of the SN in M101 near maximum, and every cloudy evening is now one more day past the peak. It's a type Ia SN, one of the standard candles by which the size of the universe is measured. That put me in mind of the cosmic distance ladder and I began to wonder if the brighter Cepheids in M31 or M33 might be within reach. While looking into that, I discovered that the AAVSO had just finished a cooperative program with the Hubble STScI people to reobserve Edwin Hubble's V1, the M31 Cepheid that settled the Great Debate over the scale of the universe in the 1920's. Hubble's Cepheid V1 varies from about magnitude 18 - 19.4 over a period of 30.41 days. The AAVSO noted that it is in an uncrowded field and was observable with CCD photometry (which was encouraging) but that (only) six observers had contributed to the light curve (which was discouraging).

aavso g


I generated "c" and "g" charts for the variable and then looked for the field in my December 2008 efforts with the 5-inch refractor and a Canon 50D DSLR (image details are on page 1 in the menu above, or just click here). I hoped to find some of the field stars to nail down the location. Instead, I found the variable itself.

Just to keep things in perspective, here's the "g" chart star-aligned over a portion of my December 2008 image of M31:


m31 CROP


And here's the juicy bit with Hubble's V1 marked. Look closely -- it's clearly there:




For orientation, the two prominent stars just above and right of the marked position are shown in the AAVSO chart as "143" and "133" (magnitude 14.3 and magnitude 13.3 with the decimals omitted to avoid confusion with field stars).

So, no, I don't think there'll be any particular difficulty getting data on V1 using a better mount, twice the aperture, and a cooled astronomical CCD.

From the AAVSO's request for observations:

The field is not crowded, and the variable itself is not blended; there are several 15-16V supergiants in the region. Contamination from the M31 background, while present, should not be prohibitive.

Coordinates:  00:41:27.30 +41:10:10.4  (J2000.0)

An R-band finder chart from the Isaac Newton 2.5-m telescope, provided by Arne Henden and showing North up, East left, and a 4.44x4.44 field of view, may be seen here.

The link to the Isaac Newton finder image is particularly useful.


9/28/2011. Here are three, 300s L exposures of the area. I stopped collecting data to refine focus and take RGB data before resuming L collection. Clouds had other ideas and the first three L frames are all I got tonight. Fifteen minutes of exposure through slightly hazy skies with a not-particularly-efficient CCD isn't quite enough. No surprise, but a bit disappointing.



M31 with V1 marked
AT10RC, ST2000XM
3x300s Baader L

The star is there, but barely. An hour or so on a clear night should produce a clean signal. I've dimmed the bright starclouds in the lower left half of the frame to emphasize foreground stars and dark nebulae in M31.


9/29/2011. The sky the next night was more transparent than any in a very long time. Seeing was not great (around 2.5 arc seconds) while tracking was spot on (after I undid a mistake in reassembing the OAG after tightening things down -- helps if the pick-off prism faces the sky rather than the sensor). With an imperfectly aligned mount (and mine is almost always imperfectly aligned) you can reduce oscillations by correcting declination drift in only one direction. This requires some trial and error, but unidirectional dec corrections work very well when the technique works at all.

V1 does show up very well with an hour's exposure. It shows up even better with four. I added color (a single set of 300s RGB) which highlighted features in M31 very well: ruddy and swirling dust clouds, the older yellow stars of the hub, drifts of bright blue supergiants in the spiral arms. Note the two associations near V1, one is full of blue supergiants and the other is wreathed with hydrogen glowing red. The image shown is downsampled for the web:


v1 color

Hubble's V1 in M31

48x300s L, 1x300s RGB
ST2000XM w/Baader filters
Astro-Phyics Mach1GTO



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                   © 2011, David Cortner