The eagle's new star
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Nova Aquilae 2009 was discovered in the constellation of Aquila on December 14th. Position: RA 19h 14m 09.73s Dec +15d 16m 34.7s (J2000.0). The star now has the official designation V1722 Aql. It is reported (by others) that nothing was visible at this location in photos taken on 6th and 7th December. It was magnitude 10.9 when discovered on 14th December.
I generated a star chart in GRIP to enable me to navigate to it from a naked-eye star, Zeta Aql. Here is the essential part of the chart, inverted so I could print it out:
North is at the top of the chart, west on the right. The nova is at the position of the cyan cross near the top left.
My photo and measurements of 2009-12-25
We have had very few clear evenings recently but I have now managed to get a photo. Aquila is only visible for a short while after dark now. It was setting behind my garden fence as I took the following picture (this is a cropped and scaled down version of the original 21 megapixels of course). The nova is at the intersection of the 2 white bars. It is not spectacular - well below naked eye visibility at about magnitude 12. None of the stars in this photo can be seen with the naked eye, hence the need for the chart.
Canon EOS5DMk2 254mm Newtonian @ 1200mm 26 x 10s f/4.8 ISO3200
2009:12:25 17:46:41-17:54:04 GMT
As usual the 26 raw photos were combined into one using GRIP's batch astro-process, fully automated (it recognises the star patterns in each frame and warps them to map onto the middle frame of the sequence). Importantly, I did not enhance the image in any way as it was saved from the 32-bit-per-channel accumulator. That was so I could go on to measure star brightnesses and estimate the magnitude of the nova by least-squares fitting of straight lines to all the measured stars (in all channels) and using the equations of the lines to calculate the unknown magnitudes. Here is the result, as saved from GRIP as a PNG image:
Notice that the star is significantly brighter in red than in green or blue. It is also evident in the photo, especially if it is further enhanced, that the nova is the reddest star in the field.
The following table lists the stars used in the graph above, their known magnitudes and their brightnesses measured from the photo. The known data were obtained by GRIP in making its star chart from the Tycho-2 database via the AstroGrid Virtual Observatory.
| Star id | Magnitudes | Brightness: Total |
Red |
Green |
Blue |
|---|---|---|---|---|---|
| 1599 2338 1 | (B)12.36 (V)11.65 | 893081 | 327596 | 548795 | 623779 |
| 1599 2691 1 | (B)10.22 (V)9.56 | 5554278 | 2288495 | 3250909 | 3878710 |
| 1599 2743 1 | (B)11.63 (V)11.22 | 1994299 | 630387 | 1200931 | 1462056 |
| 1599 3038 1 | (B)11.94 (V)11.35 | 1812874 | 820594 | 1124837 | 1160983 |
| 1599 3280 1 | (B)10.51 (V)9.76 | 4963906 | 2155045 | 2794511 | 3490968 |
| 1599 3839 1 | (B)11.19 (V)10.28 | 3719609 | 1425360 | 2213251 | 2627806 |
| 1599 3910 1 | (B)12.60 (V)12.02 | 1163557 | 423013 | 688444 | 837240 |
| Nova Aql 2009 | unknown | 903540 | 648288 | 429192 | 460329 |
When making the least-squares graph GRIP also generates a copy of the star chart in which the measured stars are marked. Here is the relevant part of the chart I used for the measurements above:
My photo and measurements of 2009-12-28
Canon EOS5DMk2 254mm Newtonian @ 1200mm 33 x 10s f/4.8 ISO3200
2009:12:28 17:26:22-17:34:44 GMT
I used the same reference stars as in the previous photo but of course their brightnesses had to be remeasured:
| Star id | Magnitudes | Brightness: Total |
Red |
Green |
Blue |
|---|---|---|---|---|---|
| 1599 2338 1 | (B)12.36 (V)11.65 | 1587993 | 666885 | 1053593 | 983326 |
| 1599 2691 1 | (B)10.22 (V)9.56 | 7420756 | 3081656 | 4892103 | 4651704 |
| 1599 2743 1 | (B)11.63 (V)11.22 | 2923269 | 1037888 | 1900485 | 1963785 |
| 1599 3038 1 | (B)11.94 (V)11.35 | 2703593 | 1322647 | 1747216 | 1583433 |
| 1599 3279 1 | (B)12.37 (V)11.86 | 1787340 | 689667 | 1190131 | 1141286 |
| 1599 3280 1 | (B)10.51 (V)9.76 | 5700151 | 2364149 | 3745134 | 3588384 |
| 1599 3839 1 | (B)11.19 (V)10.28 | 5070789 | 2240063 | 3288255 | 3143629 |
| 1599 3910 1 | (B)12.60 (V)12.02 | 2204674 | 849088 | 1435767 | 1441600 |
| Nova Aql 2009 | unknown | 1411229 | 1112120 | 651864 | 574309 |
The reference stars I have used are in fact the ones specified by AAVSO for measuring Nova Aql 2009. Tycho ids correspond to AAVSO ids as follows.
| Tycho | AAVSO |
|---|---|
| 1599 2338 1 | 000-BJS-299 |
| 1599 2691 1 | 000-BJS-290 |
| 1599 2743 1 | 000-BJS-295 |
| 1599 3038 1 | 000-BJS-296 |
| 1599 3279 1 | 000-BJS-298 |
| 1599 3280 1 | 000-BJS-291 |
| 1599 3839 1 | 000-BJS-292 |
| 1599 3910 1 | 000-BJS-297 |
Details of the measurement method
This section has moved to the more general page on how to measure magnitudes.