Doubles in Perseus - Part I
Some Doubles in Perseus - Part I
Eta Persei (η Persei)
Struve 307
RA / DEC: 02:50:42 / +55.53
Magnitude A / B: 3.8 / 8.5
Rho: 28.5”
Theta: 301º
Eta Persei, Struve 307 or Miram, lies at the northern most tip of the constellation of Perseus about 1,331 light years away. Classed as a K3 supergiant, the star is estimated to be about 11 times the mass of the sun with a diameter 105 times greater and radiating with a luminosity of about 35,000 suns. The future of the star is still unknown but it is reckoned that if it its helium has already been exhausted, then it will probably become a huge white dwarf and if it is still expanding it may explode as a supernova.
Struve 307 appears to have six or so companions, but this is probably more a line of sight coincidence rather than being all genuine secondary components. More than likely, Eta Persei has a true B and C component consisting of two B Dwarf stars.
Struve 307 is easily split at around 50x and with the ease of such magnification the contrast between the orangey supergiant and its lighter blue B companion is perfect making this a pretty and serene double to observe.
Upping the magnification to around 140x brings forth those fainter components which act as an attractive frame to the main star and it is possible to pick out not only the B companion but also Eta Persei’s C and F components. I found that with my limiting aperture averted gaze gave the best results to tweak out these fainter 10 or 11 magnitude stars. Considering I only expected to find a binary pair and ended up with a crowd made this a rather winning double.
Struve 331
RA / DEC: 03:00:9 / 52.21
A / B: 5.21 / 6.17
Rho (ρ): 11.9”
Theta (θ): 85º
The colour and aesthetic appeal of Struve 331 is as diverse as it is a mystery. Some observers claim that they see in the binary pair light shades of blue, others gentle tones of yellow, some just see a plain white pair, others a dusty blue green and hues of golden orange. Aesthetically speaking, observers have claimed anything from seeing a boring and dull binary to a spectacular showpiece. It seems, then, that the double is a bit of a cosmic chameleon and no doubt conditoned itself by the mood, disposition and quality of seeing of each individual stargazer.
Struve 331 is probably an optical binary lying some 800 light years away. Its two components are considered to be main sequence B dwarf stars which typically have a mass 2 to 16 times that of the sun and because they are burning hydrogen at such a fast rate have a surface temperture of anything between 10,000 to 30,000 k. For this reason, B-type stars are often extremely luminous and blue.
The component was easily split at 50x but gave better results around 100x. Some fainter stars can be gleaned from the dark surroundings but there is nothing here which stands out as an interesting asterism. In this fashion, coming across Struve 331 was a bit like spying two distant and frosted headlights approaching from some dark and misty wilderness.
Zeta Persei
Struve 464
RA / DEC: 03:54:1 / 31.53
A / B: 2.86 / 9.16
Rho (ρ): 12.9”
Theta (θ): 207º
Classified as a B1 supergiant, Eta Persei or Struve 464 is estimated to lie somewhere between 750 to 1,300 light years away, burning with a luminosity of anything between 47,000 to 105,000 Suns. Its sphere is around 13 to 20 times the diametre of the Sun and between 13 to 19 times its mass. Clearly, Zeta Persei is enormous.
If all the interstellar dust and gas and other cosmic debris could be removed between the star and ourselves, Zeta Persei would shine like a first magnitude star. It is probably part of the OB Associations – groupings of hot, massive and relatively short lived O or B classed blue stars which are not gravitationally bound but slowly disintegrating as the individual stars move their separate ways. At only 9 million years old, Struve 464 is a mere child-star when we consider that most stars do not begin to significantly age until they are between 1 billion to 10 billion years old and yet its fate is already sealed; the star is dying and will one day explode as a supernova.
Struve 464 appears to have four companions, two being true components (B & E) and two line of sight coincidences (C & D). The 9th magnitude B component is also a B star but is more than likely a subgiant. It orbits the A component with a distance of about 3,900 AU and takes about 50,000 years to make a full circuit. The E component is also a magnitude 9 star but probably a stellar type A about 36,000 AU away from the primary and orbiting it over a period of some 1.5 million years.
As can be seen in the sketch, Zeta Persei was sighted as bright bluish giant whilst the B companion was barely visible beyond the primary’s glare and at best with the practice of averted vision came across as a mere dot. At pretty much exactly the same position angle but farther out the D and E components were faint but clearly visible. The C companion was lost in the shining of Zeta Persei. A low 50x magnification gives the eyepiece view a more aesthetic appeal but I needed to up the magnification to over 100x to tweak out that B component.
Struve 292
RA / DEC: 02:42:5 / 40:16
A / B: 7.56 / 8.23
Rho (ρ): 22.7”
Theta (θ): 212º
There’s really not a lot of information to be found on Struve 292 and this is a shame, for one could start to believe that some of the best doubles to observe are forgotten simply because their contrast of colour or the challenge of their split doesn’t give one that immediate satisfaction. Struve 292 is probably a huge B type star about 1,000 to 1,500 light years away and with a mass of anything between 2 to 16 times that of the Sun. It may not be one of the most beautiful doubles in the night sky but as can be seen from the sketch it is a rather attractive and easily split binary set within an astonishing spectacle of other sparklers near M 34.
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