I report here on measurements of the light curve of PNV J17452791-2305213 as derived from the STEREO HI1-B observations. The photometric calibration of the telescope is described in Bewsher, D. et al., 2010, Solar Physics, 264, 433-460. The telescope response lies mainly in the red part of the spectrum between 600-750 nm, with some smaller additional response between 300-450 nm and above 900 nm. Each image is the sum of 30 individual exposures of 40 seconds each, covering the 40 minutes between each image. The brightness measurements are converted into a stellar magnitude scale by taking the ratio to the modeled brightness of Vega, as described in the above paper.
The candidate nova is first visible in the exposure centered at 15:44 UT on April 20, with an apparent magnitude of about 12.5. This number may include some contamination from a fainter nearby star which appears to be somewhere in the neighborhood of magnitude 13 or fainter. It reaches a maximum brightness of about 8.35mag around 17:44 UT on April 21, and then starts to decline. These magnitudes are somewhat lower than those reported by other observers, but this is most likely due to the dominance of red wavelengths in the HI1-B response. Spectroscopic observations of PNV J17452791-2305213 show that it is significantly reddened, and has strong H-alpha emission (CBET 3089). The full HI1-B light curve, up through May 1, is shown in the following figure. (gif, ps)
![[email address: Joseph.B.Gurman<at>nasa<dot>gov]](http://stereo.gsfc.nasa.gov/img/gurman_email.png)