June 27, 2012 1 Comment
There are now 4 (and possibly 5) novae in the Sagittarius/Ophiuchus/Scorpius region that have erupted in the past few months. Three of the 5 are still bright enough for small telescope observers.
I have been routinely observing all 5 with the Sierra Stars Observatory 0.61-m telescope. Continuing the post, 3 Relatively Bright Novae in Sagittarius/Ophiuchus, from last month, here is the latest on the novae.
Nova Sagittarii 2012 = PNV J17452791-2305213
Nova Sag 2012 has rapidly faded from its peak magnitude of V ~ 8.8. Recent CCD observations place it at V ~ 15.2 and much too faint for most visual observers. This nova is typical of most novae with a sharp peak in brightness and rapid fading. Novae are classified based on the shape of their lightcurve and the rate at which they fade. This nova faded by 2 magnitudes (t_2) in about 3 days, by 3 magnitudes (t_3) in about 6.5 days and 6 magnitudes (t_6) by about 40 days. According to the Strope, Schaefer, Henden (2010) classification scheme, Nova Sag 2012 appears to be either a S(6) or O(6) type nova. S types display smooth declines in brightness while O types show oscillations in the lightcurve. You can see hints of rapid oscillations of up to 1 magnitude during the month of May. The ‘6’ in each classification is the length of time for the nova to drop 3 magnitudes in brightness. In this case, the nova dropped 3 magnitudes from magnitude 8.8 to 11.8 in 6-7 days.
Nova Ophiuchi 2012 No 2 = PNV J17395600-2447420
Similar to Nov Sag 2012, Nova Oph 2012 No 2 also faded rapidly from a peak of ~11 to ~15.2. Assuming the earliest observations represent it maximum brightness, it faded 2 magnitudes (t_2) in 7 days and 3 magnitudes in (t_3) in 15 days. Its smooth decline makes it a S(15) nova. There was a slight brightening starting on June 14 that lasted till June 20. This could be what’s called a ‘cusp’ which is typical of the C or cusp type of nova. Usually these cusps are larger and longer lasting so the S(15) classification still seems the best for this nova.
The brightness graph below shows observations taken in 3 wavelengths, V for visual or yellow, B for blue and R for red. It is apparent that the nova is red since it is brightest in the R filter. Part of this is that much of the nova’s light is due to Hydrogen-α emission which is located at a wavelength covered by the R filter.
Nova Ophiuchi 2012 = PNV J17260708-2551454
In contrast to the 2 novae above, Nova Oph 2012 is a much slower nova. For starters the nova was first seen ~3 months ago and it still hasn’t faded by 3 magnitudes. Also it has shown numerous oscillations of almost 2 magnitudes. Currently around magnitude 12.8, the nova did appear to start fading but that fading is in question since the nova has actually brightened a little over the past week. There is a type of nova called ‘Flat’ or F types due to their long flat maximas. Nova Oph 2012 may be of this type. Only time (and more observations) will tell.
Nova Scorpii 2012
Now on to the first of the more recently discovered novae. Nova Scorpii 2012 may go down as an historic nova. The Microlensing Observations in Astrophysics (MOA) collaboration were observing the region of the sky around Nova Sco 2012 as part of their program to detect and study microlensing events (the brightening of foreground stars by lower mass objects passing between the star and Earth). An otherwise unassuming 19th magnitude (in the I band) star started a slow rise in brightness between May 14 and 16. The rate of brightening started to increase on May 24. Soon a 1.6-hr oscillation (due to the rotation period of the nova double star system?) was observed superimposed on the brightening trend. Suddenly on June 1 to 2 the object jumped 6 magnitude in brightness. Spectroscopic observations confirm the object as a slow “Fe-II” nova. Never before have the earliest days of a classical nova outburst been observed.
The nova peaked around V magnitude 9.9-10.0 on June 20. Since then it has faded to V magnitude 10.8. It is located a few degrees north of the bright open star cluster M7 at R.A. = 17h50m53s.90, Decl. = -32d37’20”.5 (equinox 2000.0).
The newest “nova” is still a ? since there hasn’t been any published spectroscopic observations confirming its nature. It was discovered by K. Itagaki with an independent discovery by Y. Sakurai (both of Japan) on June 26. I was able to observe it last night with the Sierra Stars 0.61-m at V = 9.8. The “nova” is located a few degrees to the NW of M8 at R.A. = 17h52m25s.79 Decl. = -21d26’21”.5 (J2000.0).