Double Star of the Month in Puppis

• February 2023 - Double Star of the Month

  One and a half degrees just east of the fine but unequal binary pair delta Gem (see this column for February 2013) is the pair STF 1108 (07 32 50.63 +22 53 15). The star is displayed on page 8 of the second edition of MacEvoy and Tirion's fine Double Star Atlas (CUP) but without a label. Having checked back over my file of measures I note that this pair does not appear in it, nor does it appear in my earlier visual survey carried out with a 21-cm in the late 1960s.

  

  The Washington Double Star catalogue gives the visual magnitudes as 6.6 and 8.2 whilst Gaia DR3 notes G mags of 6.3 and 8.8. There has been little motion since the pair was found by F. G. W. Struve. DR3 notes that the parallaxes are the same within the errors (and indicate a distance to the pair of 643 light-years) although these are some ten times larger than might be expected for stars of this brightness.

  Half a degree south is the unequal, wide pair 63 Gem and about a degree to the south-west is STF 1081 (7.7, 8.5, 204 degrees, 1".9, slowly increasing)

  2 Pup = STF 1138 (07 45 29.14 -14 41 25.7) lies in a string of naked eye stars which stretch about 30 minutes of RA along the line of south declination 15 degrees. Other objects in this area include M46 and M47 and the binary STF 1104 (see this column for February 2020). STF 1138 is about a degree due east of M46 and is a beautiful, easy pair for the small aperture.

  

  During a visual survey carried out in the late 1960s I found colours of yellow and lilac whereas Admiral Smyth records hues of silvery white and pale white for `2 Argo Navis'. The stars of magnitudes 6.0 and 6.7 were separated by 16".7 at PA 340 degrees when I measured them in 2015, having closed from 17".4 when measured by William Herschel in 1782.

  A third star of magnitude 10.6 lies 100" away in PA 229 and is some five times further away than the stars in the pair. They both have very precisely determined parallaxes thanks to Gaia DR3 which puts them 279 light-years away with an uncertainty of about 1 light-year.

  Bob Argyle - Double Star Section Director

• February 2021 - Double Star of the Month

  In December 1968 I was observing with friends in the back garden of a house in Newcastle-upon-Tyne using a 12-inch reflector. We looked at a number of double stars that night, including phi² Cancri = STF 1223 (08 26 47.08 +26 56 07.8) and 24 Cancri = STF 1224 (08 26 39.82 +24 32 03.7). These two pairs form a kind of wide double-double and can be found in northern Cancer.

  

  Starting with the beautiful pair iota Cancri, move about 4 degrees SE to find phi². This is a pair of magnitude 6.9 and 7.5 stars separated by 5".7 and currently at PA 53 degrees. With the 12-inch I noted that the stars appeared white and lilac at a power of x208. Gaia indicates that these stars are at the same distance from us (347 light-years).

  STF 1224 is the brighter of the two pairs with the components having V = 5.2 and 6.2. The separation is 5".2 and the position angle 219 degrees. I recorded both stars as being blue-white. Robert Aitken found that the B component was a very close binary of short period. The BC pair revolves in just 21.8 years and the separation stays close to 0".15 throughout the cycle. The Gaia EDR3 catalogue gives a parallax for the A component of 14.429 mas giving a distance of 226 light-years.

  The magnitude 2.5 star pi Puppis (07 17 08.56 -37 05 50.9) lies in a rich area of the Miky Way which is part of the Vela-Puppis star forming region. It is surrounded by a number of naked-eye stars and the open cluster Collinder 135.

  

  Pi, which is distinctly red, is a close, very unequal double star which was discovered by Hipparcos in 1991 but whose nature does not appear to have been confirmed since. Along with a magnitude 7.9 star some 67" distant in PA 213 degrees it also forms the pair DUN 43.

  To the north of pi are the bright stars upsilon 1 (V = 4.7) and upsilon 2 Puppis (V = 5.1) which are 4 arc minutes apart. Both these bright stars are variables. Upsilon 1 is also known as NV Puppis whilst upsilon 2 is NW Puppis. A V = 8.8 star lies at 119" and 215 degrees from B whilst William Jacob, observing from India, discovered a fainter companion (V = 9.1) to C at 3".1 and 209 degrees; this pair is now known as JC 10. There is another open cluster nearby called UBC7 and its possibly binary relation with Collinder 135 has been discussed.

  Bob Argyle - Double Star Section Director

• February 2020 - Double Star of the Month

  Starting at the fine pair 38 Gem (see this column for Feb. 2016) and moving 2 degrees due East, brings the observer on the pair STF 1007 (07 00 37.52 +12 43 24.2) and, a further 20 arc-mins East, upon HJ 3288.

  The brighter and wider of the two is STF 1007 which was left out of Lewis' treatise on the Dorpat pairs because it was too wide (the writer found 28 degrees, 67".4 in 2014). In fact, Burnham noted two fainter and closer companions on March 16, 1873 with his 6-inch refractor, neither of which could be seen in the 8-inch Thorrowgood with the micrometer field illumination on. C is 11.4 at 300 degrees, 15" and D is 10.0 at 244 degrees, 22" whilst Burnham called them magnitudes 14 and 12 respectively. The Washington Double Star Catalog (WDS) notes that D was found to be a close lunar occultation double.

  HJ 3288 is a pair with magnitudes 7.3 and 8.7 and the writer found 217 degrees, 38" in 2013.

  Originally found as a close bright pair by F. G. W. Struve, STF 1104 (07 29 21.91 - 14 49 53.40) turns out to be a physical quintuple system. The AB pair has magnitudes of 6.4 and 7.6 and at discovery was found at 292 degrees, 2".4. At 2017 it was 38 degrees, 1".8 and a preliminary orbit was computed by A. A. Tokovinin in 2014 who found a period of 729 years. This predicts a minimum separation of 1".7 around 2045 so the pair is always within range of 10-cm.

  In the 1880s two further stars were noted - an 11.8 at 20" (C) and a 13.2 at 72" (D). Since then D has been rapidly left behind by the considerable proper motion of AB, which is 0".3 per year. C, however, is keeping pace and is clearly physical. Dr. Tokovinin also found that C was a close pair of dwarf stars separated by 0".1 and also noted that a star 1072" away which was noted by Luyten and labelled LP 722-24, is also moving through space with a similar proper motion and distance.

  The group is 120 light years from us.

  Bob Argyle - Double Star Section Director

• February 2018 - Double Star of the Month

  Lambda Geminorum (07 18 05.61+16 32 25.7) sits in the ecliptic zone which means it can be occasionally occulted by the Moon. High speed photoelectric measurements of the star's brightness during occultation show that there is another star close in. The star is also known as a spectroscopic binary which may be the same object.

  For the visual observer the challenge is to see the faint companion discovered by F. G. W. Struve. The WDS give its magnitude as 10.7 and I can honestly claim never to have seen it. John Nanson, however, finds it slightly easier than delta and kappa Gem, which I don't, so clearly I will have to take another look this Spring.

  Lambda is only 101 light years distant and the position angle and separation, currently 36 degrees and 9".3 have changed little since the 1830s. As lambda has a significant proper motion then it seems that the faint star is travelling with it through space.

  The duplicity of 5 Pup (07 47 56.71 -12 11 33.8) is also down to Struve, and it is known as STF 1146. During the 19th century the components, of magnitudes 5.7 and 7.3, changed very slowly relative to each other but by 2016 the pair were about 1 arc second apart.

  This is a highly-inclined long-period system, like STF 1527, and the current orbit predicts a period of 1331 years and a close approach of 0".7 by 2044. At present it is well separated in 15-20cm but the difference in magnitude and low altitude in the UK sky makes the task of resolving it a little trickier. I have only been able to make two measures in the last five years.

  The surrounding area of sky is very rich. Move 3 degrees south and then swing west by 4 or 5 degrees and you will encounter more bright Struve pairs as well as M46 and M47.

  Bob Argyle - Double Star Section Director

• February 2017 - Double Star of the Month

  STF 958 Lyncis (06 48 12.23 +55 42 16.0) is a neat, bright pair in SW Lynx near the border with Auriga.

  Start by locating the bright trio of 12, 15 and 14 Lyn, all visual binaries of increasing difficulty, and move 2 degrees south of the beautiful triple 12. This brings you to 13 Lyn, an orange giant of magnitude 5.3. Move a further 1.5 degrees south and you will alight on STF 958.

  One of William Herschel's finds, it is doubtless a binary, and even although the movement since 1782 amounts a slight decrease only in the apparent separation, the WDS 6th Orbit catalogue contains two orbits computed for it. With magnitudes of 6.3 and 6.3 it is not clear which star is the brightest and even SIMBAD appears uncertain. The SB9 catalogue assigns spectroscopic duplicity to the A star and the period is given as 4.26 days. The WDS notes that the other component has variable proper motion, thus indicating that it is a physical quadruple system.

  Herschel called STF 958 A pretty double star and assigned colours of pale rose to both components. Struve, on the other hand, found both stars yellow, as did Webb in the 1850s, whilst Sissy Haas notes that both stars are khaki-white. A 11.2 magnitude star can be found 176" away in position angle 268 degrees.

  19 Pup (08 11 16.32 -12 55 37.3) is in a fairly sparse area of sky but it forms an approximate isoceles triangle with Sirius and Procyon.

  It is the bright star on the south edge of the galactic cluster NGC 2539 and not surprisingly it comes with a number of faint distant companions in the WDS catalogue.

  The primary is a G8 giant of magnitude 4.8 and small telescopes will easily show two distant companions, a magnitude 8.9 at 58" and a 9.3 a further 12" out from the primary.

  The WDS lists two more which are fainter but Burnham in 1899 found a very faint star at a distance of about 2" which became BU 1064 AB. It was also measured by Aitken but no further sightings seem to have been made since then. Van den Bos looked twice, in 1936 and 1939 without success. Steve Coe noted 19 Pup and recorded that it was a triple star with the primary yellow and the two brightest comites being white.

  Bob Argyle - Double Star Section Director

• February 2016 - Double Star of the Month

  38 Gem (06 54 38,63 +13 10 40.1) can easily be swept up since it directly follows the 3.4 mag xi Gem by a little over 2 degrees.

  The current orbital period, 1898 years, as determined by Brian Mason in 2014, is clearly very uncertain but the position for 2016.0 is 143° and 7".31 in close agreement with measures by the writer late last year. The stars are of visual magnitude 4.8 and 7.8 so the quadrant in which B lies is certainly the second whilst Sissy Haas puts it in the 4th.

  Admiral Smyth gives light yellow and purple, but E. J. Hartung sees yellowish and pale-orange, whilst to Sissy Haas the colours appear lemon-white and greyish.

  A third, much fainter star C of mag. 11.3 can be seen at a distance of 119" whilst Andrei Tokovinin noticed a 15.0 mag dot at 151". The primary, a dwarf star of spectral class F0 is 96 light years away.

  STF1121 (07 36 35.71 -14 29 00.3) is not a double or multiple star - rather it forms the bright core of the open cluster M47 in Puppis.

  This cluster was discovered by the Italian astronomer Giovanni Hodierna sometime before 1654. As well as finding a dozen or so deep-sky objects before Messier catalogued them, Hodierna also compiled a small list of double stars.

  The WDS contains 26 entries to cover this system and its large array of comites, but the small telescope user will easily be able to see AB (6.9, 7.3 at 300° and 6".5), whilst amongst the more obvious comites D is mag 9.5 at 72" (distance increasing), E is 9.9 at 70" (distance decreasing) and G is 7.7 at 82".

  It is perhaps best seen with a pair of large binoculars. A report on the Cloudy Nights website for 2004 notes that the AB pair can be split easily with Celestron 25 x 100s. M47 and nearby M46 can be swept up in a wide-field telescope by moving 20 degrees due south of Procyon.

  Bob Argyle - Double Star Section Director

• February 2015 - Double Star of the Month

  In mid-February, Gemini passes the meridian at 10pm and offers an excellent opportunity to view some of the fine double and binary stars in this constellation. One of the less-well known systems is 20 Gem (06 32 18.52 +17 47 03.4) which is eaily found about 3 degrees north preceding the bright star gamma Gem. Wil Tirion's Cambridge Star Atlas shows another double star about a degree south of 20. This is STT143 (6.2, 10.4, 103°, 7".6 with a fainter third component at 345° and 47"). Also known as STF924, 20 Gem offers a beautiful pair of stars which Webb noted as topaz yellow and cerulean blue, but as these are the exact hues noted by Smyth in the Bedford catalogue it may be assumed that Webb was merely repeating the Bedford colours. More recently Sissy Haas finds both stars to be gloss-white.

  There is little relative motion between the stars and the current situation is that the PA is 211° and the separation 20".2. Hipparcos found the determination of the parallax of star A difficult and finds a distance of 262 light years with an error of 30%. This is no doubt due to the motion induced by the duplicity of A confirmed by both occultation observations and also directly as a spectroscopic binary.

  Looking about 1° slightly north preceding the V = 4.4 star q Puppis, one will alight on the wide pairs DUN 67 (08 13 58.31 -36 19 20.2) and DUN 68 about 1.5 arc mins south and west of it. DUN 67 consists of stars of magnitude 5.0 and 6.0 which are currently separated by 66 arc seconds and PA 174°. The separation is slowly decreasing. Hartung chooses not to include them is his book 'Astronomical Objects for Southern Telescopes' but Gould with 175-mm finds both stars to be pale yellow and notes the existence of several fainter pairs in the area. The components of DUN 68 are both mag 7.3 but form a wider pair than its neighbour. The PA is 25° and the separation is 125" and increasing.

  The whole region is fine with the large scattered star cluster NGC 2546 about 1.5° further south adding further reason to take in the area with a pair of binoculars as well. Both pairs are at the same distance from us within the stated errors of the Hipparcos parallaxes.

  Bob Argyle - Double Star Section Director

• February 2014 - Double Star of the Month

  STF 1126 (07 04 06.99 31 51.9) is easily to locate - it lies in the same low power field as Procyon, preceding the bright star. Since discovery by Herschel in 1781 the stars widened slightly but at the mid-point of the 19th century they slowly began to close. Motion is very slow and at present the companion can be found at 174° and 0".9. With magnitudes of 6.6 and 7.0 this is a relatively easy object for 20-cm although being fairly low in the sky it is not often seen to full advantage. Observations by the writer with the 20-cm at Cambridge were made in 1992, 2002 and 2012 and over that period the position angle increased by 10 degrees with no change in separation. Either A or B is a spectroscopic binary according to the WDS. A third star of magnitude 11.4 can be found at 251°, 43". The primary star is an AO giant, and the catalogue value for the parallax is given as 12.6 13.7 milliarcseconds.

  STF1146 (07 47 56.71 -12 11 33.8) is also known as 5 Pup. It lies near the extreme northern border of Puppis about 3 degrees north following M46 and M47. During a winter evening of very good seeing in early January the writer made a rare foray around the stars of Puppis and saw this star well resolved with the 20-inch Thorrowgood OG. After discovery by F. G. W. Struve when separated by 3".3, the pair started to slowly close. In the 1960s Ernst Hartung noted that it was 'a fine object in a starry field and 75-mm shows it well. In recent years, however, it has been closing more quickly and now is separated by barely 1". This is a long period binary with a highly inclined orbit and the stars will reach a separation below 0".5 before widening again. Thomas Lewis gave the colours as yellowish and blue whilst Webb thought the fainter star to be ruddy in 1851. The primary star is a F5 dwarf, and this pair lies 93 light years away according to Hipparcos.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - February 2013

  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.

  It was near delta Gem (07 20 07.39 +21 58 56.4) that Pluto was first seen on a plate taken by Clyde Tombaugh at Lowell Observatory in February 1930. By a strange coincidence, Herschel found the mag 8.2 companion to delta on March 13 1781, the very same night that he discovered Uranus and later recorded the system as H 2 27. The primary star is a late A9 giant, of visual magnitude 3.55, and at a distance of 60 light years according to Hipparcos. To see the companion comfortably requires 15-cm and a night of reasonable seeing. Some disagreement attaches to the colour of the secondary. It is given as K3V in the WDS and E. Hartung noted it as reddish, as it did T W Webb but some years before he had recorded the hue of the star as purplish. The primary is also a single-lined spectroscopic binary and has also been seen double at lunar occultation’s but attempts to resolve it directly using speckle methods have so far failed.

  BU 332 (07 27 51.66 -11 33 24.7) is a multiple star which appears coincident with NGC2396 on Map 8 in Norton, close to the point where Monoceros, Canis Major and Puppis meet. Just after completing the notes on this system I read the Sky and Telescope for February 2013 and found that it featured in Sue French's column (page 57) under the name STF 1097. AC has mags 6.2, 8.7 and the components seem relatively fixed at 313° and 20". In 1865 Baron Dembowski suspected that A was double and it was later confirmed by Burnham using his 6-inch Clark refractor. Star B is magnitude 7.35 and there has been very little motion - amounting to 7° retrograde in PA, and the stars are possibly closing up. Small telescope users should be able to see the more distant D (V = 9.7) at 157o, 23". A 12.7 mag star at 32" will need at least 10-cm. Hartung notes that it is a beautiful field and that the close pair is deep yellow and white.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - February 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.

  With Gemini high in the sky in the early Spring sky, a number of binaries are on display for the small telescope user. One of the more difficult is STF1037 (07 12 49.08 +27 13 30.2), a pair of yellow stars which are locked in a highly eccentric orbit. They present a good test object because at present the separation is 1".00 according to the 116 year orbit which is given in the USNO 6th orbital catalogue. The magnitudes are listed in the WDS as 7.2, 7.3 and with the 8-inch refractor at Cambridge this pair has always been more difficult to see and measure clearly than the parameters would suggest. It is a good time to observe STF1037 - the pair is closing up again and will reach well below 0".1 in about 30 years time, and it not be this wide again until around 2063. In the 19th century, the German observer Madler was convinced that B was double again and the volume by Lewis on the Struve stars does show a loop in the apparent motion of B but no convincing evidence for a third component has come to light. Madler, and Dembowski failed to see the faint star C (V~13) found by Otto Struve. It is located at 78°, 14" but may be variable.

  Puppis is a glorious constellation for the double star aficionado and one of the best objects is k Puppis (07 38 49.88 -26 48 14.0), a third magnitude star some 8° east of delta CMa. Discovered by William Herschel (H III 27) the stars are both hot blue dwarfs of spectral type B6 and might be expected to appear white in the eyepiece. Malin and Frew, in their revision of Hartung's book thought so but noted that Hartung himself had them as pale yellow. From his observatory in Victoria, Australia this object would have passed almost overhead. Haas also calls them white but gives the star name as kappa. There has been some angular motion since 1800 - star B has moved about 8° retrograde and can now be found at 318° and 9".9. Burnham added a faint, distant star, mag 13.7 at 7" from A, but as this has not been measured since 1927, it would appear to be a difficult object.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - February 2010

  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.

  STF1127 (07 47 00.43 +64 03 07.3) is a coarse, relatively bright triple star in Camelopardalis about 90 arc minutes south of 51 Cam. The magnitudes are given in the WDS as 7.0, 8.5 and 9.7 about 0.5 mag fainter in each case than the corresponding figures in Celestial Objects for Common Telescopes. Webb notes the colours as very white, ash and orange but no other observers venture a colour estimate. The primary is A2V. Component B is 5".4 away in position angle 340 degrees almost unchanged since the early 19th century whilst C is 11".7 distant from A in PA 177. Between STF1127 and 51 Cam the neat pair STF1122 can be seen.

  HJ 3928 (07 05 32.05 -34 46 40.1) The companion star was discovered in 1836 on sweep 809 of John Herschel's 20-foot reflector, along with two more distant, much fainter (10.8 and 13.5 mag) and probably unrelated stars. AB is a binary star with the position angle decreasing from 157 degrees at discovery to 145 degrees now and the separation closing from 4.0 to 2.7 arc seconds in the same interval. The magnitudes are 6.47 and 7.81 according to the WDS so the pair should be well seen in 100-mm. Star A is 175 light years away according to the revised Hipparcos catalogue.

  Bob Argyle - Double Star Section Director

• Double Star of the Month - January 2007

  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.

  With Orion as well-placed as it gets in northern latitudes, it is worth taking a look at lambda Ori (05 35 08.9 +09 56 03) in the head of the Hunter. In binoculars, lambda forms a coarse triangle with phi 1 and phi 2 Ori. In larger telescopes and those operating in the infra-red, there appears to be a cluster of about a dozen B stars and a number of low-mass stars. Lambda Ori makes its own H II region by ionising the surrounding cool gas which appears to be in the form of an expanding ring. It may be that this is the site of an ancient supernova, some 300,000 years ago because the small proper motion of lambda itself does not project to the centre of the ring and that it may have been given a kick by a putative binary partner after that star went supernova. The young neutron star Geminga is also though to have been in that area at the time of the explosion. For the small telescope user, lambda is a fine pair with the 3.5 and 5.5 mag stars both brilliant white, reflecting their spectral types of 09.5II and B0.5V. Never less several observers have seen colour including Webb who thought they were yellowish and purple, whilst Olcott considered them yellow and red. The separation of 4".4 is virtually unchanged since records began.

  In the sprawling southern constellation of Puppis, there are many fine pairs for the small and medium telescope. A particularly noteworthy quadruple system can be found in Dunlop (Delta) 30 (06 29 49.1 -50 14 20). First listed by Dunlop in 1826 this unequally bright pair of stars is given by Hartung as yellow and reddish. The WDS lists the magnitudes as 5.97 and 7.98 and the separation is currently 12 arc seconds, making it an easy object. In later surveys, first Russell, and then the Harvard College expeditions to Arequipa in Peru found that both components were close visual doubles. The brighter component is known as R65 and has a period of 52.9 years. It is currently 0".7 apart and closing. The fainter component of the wide pair is known as HDO 195 and has a period of 101 years - it is also closing and in 2007 its separation is just below 0".4. Both systems should be resolvable in a 30-cm telescope.

  Bob Argyle - Double Star Section Director