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The eagle's new star

 

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:

Finder chart for Nova Aquilae 2009

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.

First photo of Nova Aquilae

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:

Graph showing estimated magnitude of the nova

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 idMagnitudesBrightness:
Total

Red

Green

Blue
1599 2338 1(B)12.36 (V)11.65 893081327596548795623779
1599 2691 1(B)10.22 (V)9.56 5554278228849532509093878710
1599 2743 1(B)11.63 (V)11.22 199429963038712009311462056
1599 3038 1(B)11.94 (V)11.35 181287482059411248371160983
1599 3280 1(B)10.51 (V)9.76 4963906215504527945113490968
1599 3839 1(B)11.19 (V)10.28 3719609142536022132512627806
1599 3910 1(B)12.60 (V)12.02 1163557423013688444837240
Nova Aql 2009unknown903540648288429192460329

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:

Annotated star chart showing measured stars

 My photo and measurements of 2009-12-28

Photo of Nova Aquilae on Dec 28th

Canon EOS5DMk2 254mm Newtonian @ 1200mm 33 x 10s f/4.8 ISO3200
2009:12:28 17:26:22-17:34:44 GMT

Graph showing estimated magnitude of the nova on Dec 28th

I used the same reference stars as in the previous photo but of course their brightnesses had to be remeasured:

Star idMagnitudesBrightness:
Total

Red

Green

Blue
1599 2338 1(B)12.36 (V)11.65 15879936668851053593983326
1599 2691 1(B)10.22 (V)9.56 7420756308165648921034651704
1599 2743 1(B)11.63 (V)11.22 2923269103788819004851963785
1599 3038 1(B)11.94 (V)11.35 2703593132264717472161583433
1599 3279 1(B)12.37 (V)11.86 178734068966711901311141286
1599 3280 1(B)10.51 (V)9.76 5700151236414937451343588384
1599 3839 1(B)11.19 (V)10.28 5070789224006332882553143629
1599 3910 1(B)12.60 (V)12.02 220467484908814357671441600
Nova Aql 2009unknown14112291112120651864574309

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.

TychoAAVSO
1599 2338 1000-BJS-299
1599 2691 1000-BJS-290
1599 2743 1000-BJS-295
1599 3038 1000-BJS-296
1599 3279 1000-BJS-298
1599 3280 1000-BJS-291
1599 3839 1000-BJS-292
1599 3910 1000-BJS-297

 Details of the measurement method

This section has moved to the more general page on how to measure magnitudes.

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