| Luis Argüelles, Tim Leese, Ana Fernández, Paolo Morini & John Ryan | ||||
| Star:
37 Pegasi
Date: 14th, September 2001 (2nd Meeting "Spirit of 33") Time: 22:30 - 23:30 UT Location of site: Sena de Luna, Spain 42.55N, 05 57W Seeing: 10 <1-10 Seeing Scale (10 best)> Transparency: 8-9 Other conditions: No wind. No Moon Temperature: 9ºC Altitude: 1,200 mts (3,940 ft) Site classification: Rural Sky darkness: 6.0 <Limiting magnitude> Telescopes: Vixen 4" f/10 achro refractor & Televue 101 4" f/5.6 Apo refractor Eyepieces: 35mm, 10mm and 3.8mm Baader Planetarium Eudiascopics (used on Vixen) Diagonal: Televue mirror diagonal. Used magnification for study: 263x (Vixen) Altitude of star at observing time (end): +50° 55' 11" Azimuth of star at observing time (end): 180° 39' 12" Mount used: Vixen GP Locating aids: Skysensor 2000-PC with 3 points alignment. Maximum precision. Confidence in positive identification of Star: 100% |
This tight double is located
and centered at 28x, then at 100x and finally I increase magnification
up to 263x. The star is observed for a period of time of one hour in order
to conduct an in-depth study of it.
After using every observing trick, Tim Leese and I (Luis Argüelles), observe a suspected elongation with the Vixen when the seeing is at its best. We are not using a microguide eyepiece, but perfectly agree in observing the components aligned at a "ten o'clock" position. When we speak about "suspected elongation", we are describing a sensation, a "feeling" in the limits of our experience. In fact, this is the most difficult and from the "nutcracker-class" double star I've ever observed. Very interestingly, we observe (and perfectly agree on it) a slight difference of coloration on the suspected elongated components, perceiving them as yellow and white. Ana Fernandez joins us and also agrees on this difference of coloration. Having into account the special sensitivity of Ana to coloration, confirmed by a lot of positive identifications in colors while observing doubles, we start to suspect we have got a confirmation of duplicity on 37 Peg. Nevertheless, we are not 100% sure, because the Vixen has some residual chromatic aberration, and while it only appears on the brightest stars (37 Peg shouldn't show chromatic aberration at magnitudes 5.8 and 7.1), we are afraid to make a mistake and we decide to observe again this star on next night. Spectral class: But is John Ryan who observes 37 Peg on the night of 15th, September, 2001 with his apochromatic refractor. While he is not able to observe elongation at about 180x, he confirms us the perception of colors white and yellow on this double, so we eliminate our doubts on the issue of chromatic aberration from the 4" Vixen. Very interestingly, and prior to John Ryan confirming this coloration with his APO refractor on saturday night, I rang Rafael Barberá to his home in Valencia on Saturday, 15th September morning after having breakfast in order to ask him to consult his databases for spectral classes of the 37 Peg's components. I must say that only 15 minutes later, Rafael rang me back at the Hotel in Sena de Luna, giving me data from 4 different catalogues (it's impressive how our Group works about exchanging information!). All the data were suggesting white components for this pair, so the first sensation was to think about chromatic aberration on my refractor. "What did you all drink for supper last night?", Rafa asked me in his tipical good sense of humour. "Only water for supper. We are proffesional observers, you know!" Anyway, Rafa also told me one of the components of 37 Peg is itself a spectroscopic double with the following data from the Bright Star Catalogue: Spectral Type: F5IV+F7IV, also classified A7m. K,M, met indicate A8, F1, F2 (main components at about 0.6 seconds of arc separation). Spectroscopy binary: A4, F8, ADS 15988A (Morbey and Griffin, 1987, ApJ, 317, 343) So that spectroscopic binary maybe was producing an interesting effect of coloration, but this would be a bit hard to believe hypothesis. After exchanging some e-mails on monday 17th, September, Rafa was intrigued about this issue, and researching his database of papers, he sent me in the morning of 18th September, a paper in pdf format written by Anne P. Cowley (University of Michigan) and David L. Crawford (Kitt Peak National Observatory) published by the Astronomical Society of the Pacific in 1971 tittled "Classification of some bright stars with unusual spectra". Very very interestingly, one of the stars with a revised spectra from the list inside the article was 37 Pegasi!!. The entry for this intriguing doubles reads as: Name: 37 Peg
So it seems that there is indeed a subtle difference of coloration between the main component of 37 Pegasi (it would be an A7m+F7 IV pair), and thus, producing enogh difference of coloration that would match rather well the observed yellow and white colors using our telescopes. Separation: On sunday, 16th, and using Cor's software, I simulate 37 Peg at the computer with a separation of 0.7 seconds of arc, obtaining an image close to the perception we had at 263x. Also, the apparent position angle perfectly matches the "ten o'clock" description. That figure of 0.7" would represent a Couteau's factor of about 0.5r, where r is the theoretical resolving power of a 4" telescope, and that factor would correspond to a really small elongation. But on the night of 18th
September, and using the same software, I simulate several separations
from 0.9 seconds of arc going down to 0.4 seconds in steps of 0.1 seconds
of arc. After observing the images in my computer's monitor I need to "tighten
the belts in my chair". What I observe is an excellent match between the
0.4 seconds of arc image and the observation I made of 37 Peg!!. Very excited,
I sent Tim by e-mail that set of images in order to ask him about his opinion
without telling him my judgement in order to give a no biased data. Quickly
he replied me, informing that his best match was from the 0.5 seconds of
arc image.
After that, I did some research on the Hipparcos Catalogue. Hipparcos gives the following data for separation in 37 Peg.: DC27 : 0.592 Separation from reference component, varrho (arcsec) DC29 : -0.021 Rate of change of varrho, dvarrho/dt (arcsec/yr) Since data for Hipparcos seems to have been taken in J1991.25 epoch and our observation is from J2001.75, there is a diference of 10.5 years. Taking into account the -0.021 seconds of arc variation in separation between components every year, that yields 0,221 seconds less with respect to J1991.25, yielding a preliminar result of 0.372 seconds of arc. Anyway, the Hipparcos observing interval was of 3.3 years, so there is a direct and implicit uncertainty of 3.3 * 0.021 = 0.063 seconds of arc, that in the "upper" situation would yield: 0.372 + 0.063 = 0.435 seconds of arc. And this is not far from the 0.45 seconds of arc observed mean from Tim and me! As a summary, the in-depth observation and study of 37 Pegasi offers us enough information to stay confident in identificating it as a double-star using a 4" refractor. Also, our personal guess, based on the very small perceived elongation and pattern-matching processes using Cor's software, is that actual separation between components should be around 0.45 seconds of arc. Impressive for a 4" refractor,
we think. In fact, even now it's difficult to believe for ourselves. But,
given perfect skies and concentration while observing, it's achievable.
From now on, main optics are not in the telescope for us: they are in the
sky!
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