Double Star of the Month in Andromeda

• October 2024 - Double Star of the Month

  In the north of Andromeda near the border with Cassiopeia and close to the line of zero RA lies 22 And, a star of visual magnitude 5.0. Moving about one degree west and slightly south brings us to BU 997 (00 04 57.53 +45 40 25.6), a pair of stars of magnitudes 7.6 and 9.4 and currently 3".8 apart. They should be easily seen in 15-cm although they were discovered by S. W. Burnham with the Dearborn 18.5-inch refractor. The stars show little motion, apart from a slight reduction in the pair's separation.

  

  In addition to his numbered discoveries, Burnham also noted a number of wide, faint pairs which have since been placed into the Washington Double Star catalog. One of these, BU 9001 (formerly BU 997a but renumbered to fit in with the new format of three letters and four numbers) lies about 30' due south. The stars are very unequal (6.7 and 10.6) and the companion lies at 235 degrees and 21". Larger apertures might see the 13.7 star added by Thomas Espin in 1914 at 107 degrees and 16".

  LAL 192 (23 54 21.40 -27 02 34.5) is another example of a pair being re-catalogued. It appeared in Dunlop's catalogue of 1826 as DUN 253 but was apparently changed to its current moniker at Lick Observatory when the double star catalogue existed on index cards but no-one seems to know why. It is, in any case, well worth seeking out. Easily seen in 10-cm the 6.8 and 7.4 magnitude components are presently 6".5 apart, a distance which is slowly increasing. Ross Gould using 10-cm records colours of pale yellow with a slight difference in shade.

  

  LAL 193 is in the neighbourhood. It is 1.5 degrees ENE of LAL 192 and the magnitude 6.2 SAO 192262, a distinctly orange-hued star lies between the two. LAL 193 consists of two early-F dwarfs of magnitudes 8.1 and 8.3. The current separation and position angle are 19".4 and 169 degrees and they also appear to comprise a physical system.

  Bob Argyle - Double Star Section Director

• November 2023 - Double Star of the Month

  In the western reaches of Andromeda, about 10 degrees north of the faint naked-eye shape of Triangulum sits the glorious double star gamma Andromedae (see the entry for Dec 2006).

  Move 3.5 degrees SSE and 59 And (02 10 52.83 +39 02 22.4) will appear in the field of view. This is a fine pair for the small telecope, the magnitude 6.0 and 6.8 components being currently separated by 16".6 and position angle 36 degrees.

  

  Although it is usually known as STF 222, it was noted by William Herschel in July 1783. He noted the stars were reddish white and pale red and catalogued it as H 4 129. Herschel also noted a third star in view about 58 or 60 degrees south proceeding. In 1968 I noted a `superb' pair with colours of white and lilac. More recently Sissy Haas calls the colours of the stars pearl white and peach white.

  Gaia puts both stars at the same distance within the observational errors - 438 light-years.

  The United States Naval Observatory in Washington has a history of carrying out stellar astrometry which stretches back 150 years. During this long history they have occasionally noted new double stars which appear in the Washington Double Star catalog (WDS) under the catalogue name WNO.

  The first entry in this list, WNO 1 (00 53 12.46 -24 46 37.0), was found in 1876 and is a rather unequal pair (6.6, 8.9) which has moved very little since the first measurement. It is currently at 7 degrees and 5".4.

  

  The pair lies in Cetus about 1.5 degrees ENE of the bright spiral galaxy NGC 253. About 2.5 degrees N of WNO 1 is STN 3, another pair worth looking at. It has been closing since discovery in 1877 - 7.6, 8.4, 240 degrees, 2".

  Bob Argyle - Double Star Section Director

• October 2023 - Double Star of the Month

  About 15 degrees north of the centre of the Square of Pegasus is a relatively sparse region of stars but it does contain some interesting doubles. Near the south end of this space is STF 3050 (see this column for October 2016) whilst four degrees further north and slightly preceding is STF 3042 (23 51 52.409 +37 53 28.4) which consists of stars with magnitudes 7.6 and 7.8 and which are currently 6" apart at PA 87 degrees. I found them to be a delightful pair of yellow stars whilst the entry in Sissy Haas' volume notes them as an easy white pair.

  

  They likely form a long period binary as Gaia DR3 notes that the parallaxes differ by just 0.009 milli-arcsecond. The stars lie 226 light-years away and both appear white, but are contrasted against an orange star 3' to the south-east. Unrelated to STF 3042 this is the long period variable candidate V 397 And (V = 8.9) which was picked up by Hipparcos. The listed amplitude is just 0.03 magnitude, and the spectral type is M5.

  Move 2.5 degrees west and slightly south to find the unequal pair STT 501. The stars are 6.5 and 10.6 and have PA 162 degrees and separation 15".

  41 Aqr (22 14 18.02 -21 04 28.9) sits four degrees north of the Aquarius—Piscis Austrinus border and is just four degrees west of NGC 7293 the Helix Nebula.

  

  It is number 56 in William Herschel's third double star list and is an easy pair for the small aperture. The stars have magnitudes 5.6 and 6.7 and the primary is a KO giant; a rather ambiguous note in the Washington Double Star catalog (WDS) implies that it has a composite spectrum which is strengthened by the fact that Gaia DR3 quotes an error in the parallax about three times higher than might be expected for a star of this magnitude. The stars have similar parallaxes and proper motions and as the parallax of the companion is more precise then both stars must lie 239 light-years away.

  This is a pretty pair; Smyth recorded colours of topaz yellow and cerulean blue whilst Webb noted reddish and blue and Sissy Haas yellowish-peach and pale violet.

  The WDS also notes two more distant and unrelated field stars: an 8.9 at 45 degrees and 210" (C) with another fainter object of V = 11.6 12" away from C in PA 255 degrees.

  Bob Argyle - Double Star Section Director

• November 2022 - Double Star of the Month

  In the corresponding column for this month in 2021, I mentioned a number of pairs close to the bright, close binary phi Andromedae. As promised this piece will include the pairs MAD 1 (01 00 35.58 +47 19 14.6) and STT 21 (01 03 01.54 +47 22 34.1).

  

  STT 21 is about 1.5 degrees west of phi And and is now considerably easier to observe than in the 1840s when the separation was 0".6 The current orbit of 450 year period was published by W. D. Heintz in 1966 and predicts a position of 176 degrees and 1".2 for late 2022. The apparent orbit is one of high eccentricity and inclination and the apparent motion appears to be almost linear. The magnitudes are 6.8 and 8.1 and the pair should be resolved in 15-cm aperture.

  Johann Madler (1794 - 1874) succeeded F. G. W. Struve as Director of Dorpat Observatory where the main instrument was Fraunhofer's 9.3-inch refractor with which Struve had carried out his great survey of double stars. MAD 1 can be found half a degree west of STT 21. It is a long period binary with main components of magnitudes 7.7 and 9.1. When first observed the separation was 1" but the stars have been closing slowly and at the present time are 0".74 apart in PA 356 degrees, if the 2127 year orbit currently in the catalogue is accurate.

  HJ 5437 (00 00 34.35 -53 05 51.8) sits in southern Phoenix 20 arc-minutes to the south-east of the red giant pi Phe (V = 5.1).

  

  It is not labelled in the second edition of the Cambridge Double Star Atlas, and was found by John Herschel in 1836 at 340 degrees and 2".5 since then has been slowily closing. In 2019 the stars were at 340 degrees and 1".4 and as the magnitudes are respectively 6.9 and 9.9 this is a rather difficult pair which probably needs at least 20-cm.

  Although the observed motion only amounts to 44 degrees, a premature orbit with a period of 904 years is listed in the online USNO 6th orbit catalogue. Incidentally the USNO double star website is back on-line and can be found at crf.usno.navy.mil. The WDS catalogue is available again but the latest update appears to have been about 2 months ago.

  Bob Argyle - Double Star Section Director

• October 2022 - Double Star of the Month

  Just to the north-east of the Blue Snowball Nebula, NGC 7662, in Andromeda is an asterism of naked-eye stars in the shape of a `Y'. The star at the position where the figure forks is kappa And and just half a degree to the west is STT 500 (23 37 32.53 +44 25 44.5).

  

  This is a long-period binary, a preliminary orbit computed in 1981 gives a period of 351 years, and an aperture of 25-cm is probably needed to divide the stars. The V magnitudes are 6.1 and 7.4 and when the binary nature of the system was discovered in 1843 by Otto Struve at Pulkovo, the stars were 0".3 apart and at a position angle of 273 degrees. They are currently separated by 0".4 and they have moved around to a position angle of 21 degrees.

  Gaia DR3 has an entry for the brighter star but no data on parallax and proper motion. The Hipparcos satellite gave a distance of 807 light-years but with a formal error of 104 light-years. At a distance of 118" and a position angle of 334 degrees is a more distant star of V = 11.0.

  DUN 249 (23 23 54.52 -53 48 31.5) is located in the extreme SE corner of Grus and about 2.5 degrees due east of kappa Gruis. Like many other pairs in the Dunlop catalogue this is a wide and bright pair, easily seen in the smallest of apertures. I measured it using the 26.5-inch refractor at Johannesburg in 2016 when the position angle and separation were 211 degrees and 26".4 respectively.

  

  Gaia DR3 gives distances of 408 and 494 light-years for the stars which, nevertheless, have very similar proper motions. The errors on the parallaxes nowhere near overlap so it seems that these stars are not connected physically.

  Head 3 degrees north and there is a line of DUN pairs stretching along the 51st parallel of south declination including DUN 246, DUN 248 and DUN 250.

  Bob Argyle - Double Star Section Director

• November 2021 - Double Star of the Month

  On the border of Andromeda and Cassiopeia, about 15 degrees north-west of gamma And, is the naked-eye star phi And (01 09 30.12 +47 14 30.6). This has long been known as a close and difficult visual binary, having been discovered by Otto Struve at Pulkova in the 1840s.

  

  The orbital period is long, a recent estimate put it at 554 years, but at present it is slightly wider than 0".5 and is thus within range of 25-cm, although 20-cm might well show an elongation. The stars are not equally bright, the Washington Double Star Catalog (WDS) gives values of 4.6 and 5.6 for the magnitudes.

  Within 2 degrees of phi there are three other double stars marked in the Cambridge Double Star Atlas, 2nd edition. Two of these (MAD 1 and STT 21) will be discussed in this column next year.

  The other is BU 397 which lies 40' south-west of phi. The stars are magnitudes 7.5 and 10.3 at PA 142 degrees and separation 8".7. This pair was actually discovered by John Herschel, but S. W. Burnham noted that Herschel had made an error of 1 degree in declination. Burnham also added a fainter and more distant star - 12.9 at 72 degrees and 19".3.

  66 Cet (02 12 47.54 -02 23 37.1) is a beautiful wide pair to be found 1.5 degrees WNW of Mira Ceti, the famous long period variable star. Mira reached maximum brightness in August 2021, so judging by previous light curves it is expected to be about V = 7.5 by mid-November.

  

  66 Ceti has stars of spectral types F8V and G1V and visual magnitudes 5.7 and 7.7. The position angle of 235 degrees and separation of 16".8 has remained unchanged since 1783 when the pair was noted by William Herschel. This is almost certainly a physical pair, since in addition to very similar parallaxes the two stars have the same considerable proper motion.

  In addition, the A component, which was known to be a spectroscopic binary, has recently been resolved by Dr. Andrei Tokovinin at Cerro Tololo using the 4 metre SOAR telescope, The period is 94 days and the angular separation is under 0".02.

  A more distant star of V = 11.5 is optical. I found the primary stars to be yellowish and lilac with a 21-cm reflector.

  Bob Argyle - Double Star Section Director

• November 2019 - Double Star of the Month

  STF 79 (01 00 03.56 +44 42 47.7) This is a beautiful, easy pair in Andromeda about 4.5 degrees north-east of M31. It was missed by William Herschel on his first two surveys for new double stars but swept up eventually in 1786 and is catalogued as H N 45.

  Sissy Haas notes that the stars are pearly white and pale blue-violet. When I last observed it in 1968 I recorded it as 'bluish-white and bluish(?)' in a 21-cm reflector at x96. Strangely it has not been measured with the Cambridge telescope at all, although an easy object and with the stars of magnitudes 6.0 and 6.8, and the current position is 195 degrees and 7".9.

  An image of the pair appears on the Asociacion Astronomica de Hubble website. The observer JCS noted that the stars appeared to be a delicate shade of sky-blue and there did not appear to be any contrast between them.

  Both stars are spectroscopic binaries and probably form a quadruple system. DR2 places them 494 light years away.

  H 2 58 (01 59 00.72 -22 55 11.2) is in Cetus, about 0.5 degree south-east of 56 Cet. It is one of William Herschel's discoveries. He noted that the stars were considerably unequal but the WDS gives 7.3 and 7.6 and Gaia gives a magnitude difference in the G band of just 0.17. Herschel also gave both colours as dusky white and the spectral types are A7 and G0 according to the WDS.

  Found at 315 degrees and 5".0 in 1782, the stars had widened to 8".3 in 2015 with the PA decreasing to 302 degrees. More recently, the primary was found to be a W UMa ellipsoidal eclipsing binary system which is now known as AA Cet. The period of variation is 0.536 days and the magnitude range is 6.2 to 6.7. Both stars are given as F2 in the Catalogue of Eclipsing Variables by Avvakumova (2013).

  Bob Argyle - Double Star Section Director

• October 2016 - Double Star of the Month

  STF3050 (23 59 29.33 +33 43 26.9) is a beautiful pair of white stars forming a long period binary system to the north of the Square of Pegasus. More specifically, it is 5 degrees north of and 2 degrees preceding Alpheratz (alpha And).

  The components are mags 6.4 and 6.8 and the spectral type of star A is F8V, whilst that of B is likely to be similar. The first observation in the WDS is for 1777 representing the discovery of the system by Christian Mayer. It is the 80th and last entry in his pioneering double star catalogue. William Herschel later recovered it on December 13, 1787 and called it H N 58.

  Thomas Lewis in his book on the Struve stars published in 1906 said it was evidently a binary, whilst Burnham in his General Catalogue of the same year notes apparently rectilinear motion. Subsequent observations have proved Lewis right and the pair is now significantly wider than it was at the beginning of the last century when it closed to less than 2". An orbit produced in 2011 by W. Hartkopf predicts a period of 717 years, with a position in late 2016 of 340 degs and 2".4. This makes it an easy target for 75-mm apertures and above.

  Lewis noted that both stars were yellowish.

  Beta PsA, (22 31 30.33 -32 20 45.9) bemoans Jim Kaler on his Stars website, is a neglected object most likely all alone, apparently unloved by a companion, or, for that matter, by astronomers and he compares it unfavourably with the much more referenced star alpha PsA.

  Beta is certainly a fine double star and worth a visit, and the question of whether it is binary or not can be settled by considering the proper motions of the two stars.

  The Hipparcos satellite reveals than A (mag. 4.3) is 143 light years away and moves across the sky, mostly to the east, at about 60 milliarcseconds per year. Star B has an almost identical proper motion and radial velocity and so is physically connected to A. Over the last 200 years the separation has reduced from 35".3 to 30".6 and the PA is almost fixed at 172 degrees.

  The SIMBAD spectral types of A1 and G1 might suggest stars of white and pale yellow when in fact the observed colours (by Hartung) are given as pale yellow and white, although he notes that B sometimes appears reddish.

  Bob Argyle - Double Star Section Director

• November 2015 - Double Star of the Month

  56 And (01 56 09.23 +37 15 06.5) is a very wide pair of stars which can be found 5 degrees south and a little preceding that spectacle of the autumn sky, gamma Andromedae.

  It is notable for the colours of the stars involved.

  Here we have a K0 giant (A) and an M0 giant (B) within 200" of each other but actually not associated at all. The M star is about 3 times further away than the other according to Hipparcos.

  Although the WDS gives visual magnitudes of 5.7 and 6.0, historical reports sometimes put star B as the brighter of the two - it is likely that either or both stars are liable to some small variation in brightness of a size such as to blur the difference between the two altogether.

  Burnham, who would have been interested in this system because of the large proper motion of A (0".2 per year), found a faint companion of mag 11.9 at 18" and 77 degrees from A.

  Also nearby (two-thirds of a degree preceding and a little north, according to the discoverer William Herschel), is STF 179, containing stars of magnitudes 7.6 and 8.1 separated by 3".5, and the open cluster NGC 752 is less than a degree north following.

  Bernhard Hildebrande Dawson was an Argentine astronomer who was born in Kansas City in 1891 and who worked initially at La Plata Observatory in Argentina. He was perhaps best known as the discoverer of Nova Puppis 1942.

  His double star discoveries are denoted by a small greek delta and number 31 is perhaps his most interesting find - a visual pair with a period of 4.56 years.

  He started using the 17-inch refractor at La Plata in 1912 to pursue a programme of re-measurement of the John Herschel pairs. The first star in his catalogue (DAW 1 at 02 27 57.34 -58 08 22.3) was found in 1916 and sits in a rather blank area of sky in Horologium about 13 degrees following the first magnitude Achernar. This is a triple system with the two widest components (17" apart) being found by Sir John Herschel in South Africa.

  In 1916 Dawson divided A and found a separation of 0".8. The current value is 1".2 so assuming it is still widening this would explain why Herschel did not see it during his sweeps.

  The WDS gives A and B as 8.0 and 8.5 whilst C is 9.6. The range of position angle of AB is close to 180 degrees, a sign that the magnitudes of the two stars must be close enough to cause uncertainty about the quadrant in which B sits.

  Ross Gould from Australia using a 40-cm sees A as a bright yellow star whilst x140 will show the Dawson companion.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - November 2011

  In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.

  The constellation of Andromeda now rides high in the evening sky stretching across some 50 degrees of right ascension. One of its most famous double stars is gamma (see DSOTM for Dec 2006) but some 6 degrees north of gamma and slightly following is the binary system STF 228 (021402.43 +472903.3). The spectral types of the stars are given as F2V and F7V in the WDS with visual magnitudes of 6.56 and 7.21. The period is 144 years and at present the separation is beginning to decrease with the relative position for 2012.0 given as 295°, 0".8. By 2032 the distance will have reached 0".32. Hipparcos gives the parallax of 25.23 milli-seconds of arc (mas) with an error of 0.66 mas which places the system at a distance of 129 light years.

  Whilst Andromeda is one of the largest constellations, Reticulum (The Net) is one of the smallest. Extend a line from alpha through delta Reticuli a little more than the separation of those two stars and you come to Dunlop 14 (033810.24 -594635.0). Visible in binoculars it repays examination through the telescope. The two stars, magnitudes 7.00 and 8.34, are both main sequence F stars and yellow in colour. Their separation was 45" at discovery in 1826 and by 2008 this has increased to 57".4. However, looking at the Hipparcos Catalogue reveals the fact that both the proper motions and parallaxes of the two stars are identical to within the given errors which makes this a bound system and it is located about 247 light years away. In Sissy Haas's book Double Stars for Small Telescopes, Ross Gould observing from Canberra with a 7-inch refractor, noted a faint third star of magnitude 12.8 close to B and which is not yet in the WDS.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - October 2008

  In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.

  This month's pairs ar both bright, well-observed binaries and well seen in small to medium apertures.

  36 And (00 54 58.02 +23 37 42.4) is a beautiful pair following the Square of Pegasus, some 3 degrees south following zeta Andromedae. The two stars are strong yellow (Webb) or golden (Smyth) and form a binary system whose period is 167.7 years so it has passed the position it occupied when discovered by F G W Struve in 1827. The current PA and separation are 322 degrees and 1".1 making it a fine sight in a 15-cm telescope. It is strangely absent from Hartung's book, which includes more northerly objects of less distinction such as AC 1. This system is almost 38 pc distant and the primary is a K1 subgiant. The star itself is just visible to the naked-eye with the components being magnitudes 6.1 and 6.5.

  p Eri (01 39 47.24 -56 11 47.2) is one of Dunlop's discoveries (Dun 5) and is probably the nearest equivalent to 61 Cygni in the southern hemisphere. It is close (5.3 parsecs according to Hipparcos), it contains two K dwarfs (in this case K0 and K5) which have visual magnitudes 5.8 and 5.9 respectively, has a similarly long period (483 years) and is also well-separated - reaching a maximum distance of 11.8 arc seconds in 2040. The Chambers edition of Smyth's Celestial Objects which contains a southern extension, also identifies the star as 6 Eri but does not mention colours, neither does John Herschel in his Cape observations. Hartung records both as deep yellow.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - December 2006

  In this new series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.

  gamma And (02 03 53.9 +42 19 48) is one of the most impressive double stars in the northern hemisphere. It first appears in the list of pairs found by Christian Mayer and published in the Astronomische Jahrbuch in 1784. William Herschel first measured it in the late 1770's when he found 70.4 degs and 9".25 `a mean of two years observation'. The colours are striking - yellow and blue green, the latter a contrast effect - reflecting the spectral types of K3 and B8. The relative positions of the two bright stars has changed little since then - the modern values being 63 and 9.5 In 1842, Otto Struve, using the new 15-inch refractor at Pulkova found the companion to be a close pair. Subsequent observations show that BC is a 61 year binary with a highly inclined and eccentric orbit, closing from 0".4 at discovery to become single in all telescopes by 1892. It is currently closing again (the latest orbit showing 0".33 for 2007.0); between 2014 and 2016 it will swing through 280 degrees of position angle and then start to widen again, having reached a minimum distance of just over 0.01 arc seconds in late 2015. This may be the last opportunity for some time for owners of 25-cm telescopes to see the pair elongated.

  theta Eri (Acamar - 2 58 15.7 -40 18 17) is a brilliant white A star some 20 degrees north following Achernar (alpha Eridani). The parallax as determined by Hipparcos is 20.72 mas yielding a distance of 157 light years. The small proper motion of about 0.06 arc seconds per year of star A would have changed the separation of the pair by some 10 arc seconds over the last 200 years. No such change appears in the relative measures so the pair is clearly a long period binary. The WDS shows that the PA has changed by 8 degrees between 1835 and now whilst the separation has edged closer from 8".7 to 8".4. The notes to that catalogue also indicate that the primary star is a spectroscopic binary but it does not appear in the 9th Spectroscopic Binary Catalogue. The WDS has it under the catalogue name PZ 2 and in Piazzi's Praecipuarum Stellarum Inerrantium Positiones Mediae of 1814 the stars are given magnitudes 4.5 and 5.6. The modern magnitudes are 2.9 and 4.0. The fainter star of this beautiful pair is also an A star so both components appear white. It is visible in small telescopes and possibly larger stabilized binoculars. It reminds the writer of the pair theta Aql.

  Bob Argyle - Double Star Section Director