37 Pegasi

Otto Piechowski
Star: 37 Pegasi
Date & Time: Sept. 1, 2001, 12:30 AM EDT
Seeing: 6 <1-10 Seeing Scale (10 best)>
Location of site: Lexington, KY, USA
Site classification: suburban 
Sky darkness: 4 <Limiting magnitude>
Temperature: 60º F., still, some humidity
Telescope: 150 mm Mak-cass
Eyepieces: 11.4mm, 7mm, 5mm, 4mm

Star: 37 Pegasi
Date & Time: 10:00 PM EDT, October 17, 2001
Seeing: 8-9 <1-10 Seeing Scale (10 best)>
Location of site: Lexington, KY, USA
Site classification: suburban 
Sky darkness: -- <Limiting magnitude>
Telescope: 150 mm Mak-cass
Magnification: 450X, 720X, 900X

I am not sure.  From time to time it felt like a faint bluish star was huddled next to  the primary in or near one of the diffraction rings.  But then, with instability of the atmosphere it would totally disappear.

A little touch of elongation, perhaps in an east west direction, maybe a bit more of an east by northeast direction.

Richard Harshaw 
Star: 37 Pegasi
Date & Time: September 5, 2001,
0230 to 0510 UT
Seeing: 6 <1-10 Seeing Scale (10 best)>
Transparncy: 6 to 7 (variable, due to high hazy clouds) <1-10 Seeing Scale (10 best)>
Location of site: Northern Kansas City,
Missouri (USA). 39º15' N, 94º30'W
980 ft above Mean Sea Level
Site classification: suburban 
Sky darkness: -- <Limiting magnitude>
Telescope: Celestron C-8, C-11
Magnification: 112x, 207x, 560x
Harshaw Scale: 5 <1-5; 1 best>
STF 2912  (Alias 37 Peg)
HD Number 213235
ADS 15988
Position:  2230+0426  Rating:  5
 A:  5.8m, F5 IV
 B:  7.1m, F2 V, 1 +” @ 116 + 
Year of last AB Measure:  1969
Distance (l.y.): 172, Luminosity (Suns): 14.6
Observed colors:  W, W 

Observations: C8: Observed at 207x.  Notched.
C11: Observed at 560x.  W and yW.  At 112x, I noted that this star was oval in shape.  The seeing was not steady, so at times I got a clean split at 560, and at other times, a little "snowman".

Notes: First measure (1831) by F. W. Struve:  1.2" @ 113.  1911 (Bryant), 0.3" @ 112.
The orbit takes 140 years (Knipe, 1960), and is about the diameter of Pluto's orbit.   Its plane is almost exactly in our line of sight.  It could not be resolved in 1914-1916, and were widest in 1980.
Star A is a spectroscopic binary (372.4 day period).

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
Visual Magnitude: 5.5
Bright Star Catalogue Spectral Type: F5 IV
Revised Spectral Type: A7m

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.


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!

Jim Phillips
Star: 37 Pegasi
Date & Time: Oct. 3th, 2001, 8:30-9:30 EDT
Seeing: 7 <1-10 Seeing Scale (10 best)>
Location of site: Charleston, South Carolina, USA
Site classification: Suburban.
Temperature: 70ºF
Sky darkness: --- <Limiting magnitude>
Telescope: AP 155 F/7 Apochromat
Magnification: 214x, 343x

Star: 37 Pegasi
Date & Time: Oct. 4, 2001, 8:00-9:15 EDT
Seeing: 7 <1-10 Seeing Scale (10 best)>
Location of site: Charleston, South Carolina, USA
Site classification: Suburban.
Temperature: 70ºF
Sky darkness: --- <Limiting magnitude>
Telescope: AP 155 F/7 Apochromat
Magnification: 343x, 429X

Whew! Not sure I was able to see anything except possibly a slightly elongate image.

An all out assault using all eyepieces and barlow. With 10mm (343X) I thought I could elongate the image. Not a figure 8 just a little elongate. At 429X (16mm plus 2x 
Barlow) the image was pulsating, rarely settling down for just a second or two. Again, I thought it was "slightly" elongate. Not sure. Star appeared slightly yellowish but I could not attribute that to a secondary.

Ambience: A few mosquitoes buzzing around.

William Schart
Star: 37 Pegasi
Date & Time: October 7, 2001
2123 and 22:00 CDT
Seeing: 7 <1-10 Seeing Scale (10 best)>
Location of site: Killeen, Texas, USA
Site classification: Suburban.
Sky darkness: 4 <Limiting magnitude>
Telescope: Celestron-8
Eyepieces: 25mm, 10mm, CMG
Magnification: 80x, 200x, 165x
I broke the order of the list to take a look at this, since it has generated much traffic of late. At high power it was elongated somewhat, but not cleanly split. I think that I need to tweak my collimation somewhat, but not tonight. It appeared yellow.


PJ Anway
Star: 37 Pegasi
Date & Time: Oct. 11, 2001  02:00 UT
Seeing: 6, with brief moments of 7 to 8 <1-10 Seeing Scale (10 best)>
Location of site: Munising, Michigan, USA
Site classification: Rural
Sky darkness: 5.8 <Limiting magnitude>
Sky condition: No moon or clouds, extensive Aurora activity
Temperature: 41°F   5°C
Telescope: Celestron C11, f/10 & Zeiss AS 100mm, f/10 refractor
Eyepieces: Vixen  25mm, 12.5mm, 9mm, 7mm orthoscopics & 2.4X barlow
C11: 112X & 224X
AS 100: 111X, 143X,  266X & 343X
37 Pegasi was easy to locate just a little southeast of Theta.
I began with the C11 for the most "fire power", but soon realized that with it, the seeing would not bear more than 200X.

I then switched to the 4" hoping the smaller aperture would fair better by trying to sneak between the atmospheric cells........ it did. However, as I worked my way through the eyepieces, first at 111X and 143X, then barlowed to 266X and 343X, I soon realized the  brief moments of steadiness were to short to study a double of this small separation for duplicity. No split at this time, will try again when the sun is more cooperative and a night of better seeing would also help.

Luis and Tim - I appreciate even more your accomplishment at Sena de Luna!


Thad Robosson
Star: 37 Pegasi
Date & Time: Saturday, Oct 13th, 2001
Seeing: 6.5 <1-10 Seeing Scale (10 best)>
Location of site: "All Arizona Star Party"
32º27.687N, 111º 43.787 W
Site classification: Rural
Transparency: 7 <1-10 Scale (10 best)>
Sky darkness: -- <Limiting magnitude>: 
Telescope: 8" f/6 reflector
Magnification: --
While attending the All Arizona Star Party, I attempted the "challenge" object 37 Pegasi.  This sub-arcsecond ( .6" I believe) pair was spied as a double by a trio of observers in Sena de Luna, Spain with 4" refractors in seeing of 9~10.  I keep hoping that either I get seeing that good, or that 8" of aperature will make up for it.  No such luck this time, the seeing never really allowed me to get above 125x for this point source object.  I still have a month or so before I'm banished to next year's round of attempts.


Tim Leese
Star: 37 Pegasi
Date & Time: 12,18/October/2001
22:00-23:00 UT
Seeing: 6-7 <1-10 Seeing Scale (10 best)>
Location of site: Northwich, Cheshire. UK.
53° 15' N -2º 33' W
Site classification: Suburban
Conditions: Clear spell with drifting high haze.
Sky darkness: 3.0 ( UMi ) <Limiting magnitude>
Telescope: 200mm f/6 Newtonian reflector mounted over a Vixen GP mount (manual slow motion).
Eyepieces: 5mm Vixen Lanthanum, X2 shorty barlow.
Magnification: X240, X480
I attacked 37 Peg  using my Vixen Lanthanum, giving X240 magnification, keeping the star in view  for as long as I could by letting it drift across the FOV many times. I couldn't split 37 Peg into its components but got a
definite impression that the star wasn't completely circular.
I later compared the view with 35 Peg nearby which was completely circular in the view. 37 Peg appeared to be a white colour through this scope at this magnification. Observing at this magnification I got the impression of slight elongation ( ten past the hour // twenty to the hour ).
Increasing the magnification to X480 gave a very unsteady view at times but with time and patience I observed what could be described as a rod for this star at the same position angle. These were only fleeting glimpses in the microseconds of steady air but I managed to get a good impression.
The colour at this magnification was hard to determine but I got an
impression of white with a subtle change to cream at one end of the rod.