2013 has seen two moderately bright novae, V339 Delphini at around 5.0 visual at maximum and V1369 Centauri at magnitude 3.5 in early December and a similar level two weeks later. At the New Year it was hovering around 4.3 and maybe rising in brightness again. The Delphinus nova was a normal fast nova, not extreme, but has now faded to V = 11 but our southern object seems to be quite unusual in behaviour and worthy of as much attention as we can manage.
What makes a nova? In simple terms it occurs when accreted hydrogen in a CV binary system is forced into the degenerate regions of the white dwarf component – where temperatures of over 107K allow nuclear fusion. Since this region extends quite close to the surface the energy release is explosive and a shell is ejected at velocities of from 500 to 2000 kilometres a second. Sometimes this shell is reasonably symmetric as appears to be the case with V339 Delphini, but it may be clumpy and distorted as looks likely for the Centauris nova.
Much of our understanding of novae is based upon historical visual and photographic light curves, supplemented by spectroscopy with large telescopes. But times have changed and the last half century has seen the development of detectors with a wide range of wavelengths and more efficient spectrographic equipment. More importantly, this equipment is relatively inexpensive and simple to use, which sees a welcome involvement of amateur observers of all kinds – visual and DSLR, CCD, spectroscopic.
We’d like any of our participants who are observing Nova Centauri 2013 to place their observations on this website as a permanent record of an important astronomical event. Naturally these will be discussed and shown on the Google email system as well and updates will appear in the Newsletter. The goal is to present these in the form of a formal, refereed paper, or papers, at appropriate times. So members, let’s make this a very successful project.
Simultaneous acquisition of BVR magnitudes and the wide field of view available when using telephoto camera lenses make DSLR photometry the technique of choice for V1369 Cen while it remains relatively bright (approximately <10 in V, <9 in B and R).
Extinction corrected and transformed measurements in BVR are requested.
Evolving emission line features in the spectrum of V1369 Cen will affect the accuracy of these magnitudes because B and R filter pass bands in DSLR cameras are significantly different to photometric B and R filters. Never-the-less, your DSLR observations will be valuable contributions to our understanding of this unusual nova.
For those who wish to use it, an Excel spreadsheet (Modified CSIS Spreadsheet) is available to convert their instrumental magnitudes to extinction corrected transformed BVR magnitudes. An ensemble of six Comparison stars is required to use this spreadsheet and the accompanying Finder Chart shows the currently recommended Comparison and Check stars. A Modified CSIS User Guide for the spreadsheet gives step by step instructions for its use.
Finder Chart and Sequence
DSLR cameras have lower dynamic range (14 bit) compared with astronomical CCD cameras (16 bit). Therefore Target, Comp and Check stars should all be within a range of about 2.5 magnitudes. Some older model DSLR cameras are 12 bit and may require image stacking to achieve suitable signal to noise ratios.
The following table lists details of the Check and Comp stars recommended while V1369 Cen remains relatively bright. These stars are shown on the accompanying finder chart which is an image recorded with a 200mm lens set to f3.2 and defocused to avoid saturation of Target, Check and Comp stars.
The data (except R catalogue magnitudes) are from Guide9, magnitudes are transformed from the Tycho 2 catalogue. The R Cat values were calculated from (B-V) Cat values using calibration formulae from Caldwell et al. 1993, SAAO Circulars, 15, 1-29.
|Star||RA (deg)||DEC (deg)||B Cat||V Cat||R Cat||(B – V) Cat|
|Comp 1||HD 122438||210.861||-56.213||7.133||5.925||5.308||1.208|
|Comp 2||HD 123335||212.234||-59.277||6.357||6.342||6.330||0.015|
|Comp 3||HD 122879||211.605||-59.716||6.490||6.432||6.394||0.058|
|Comp 4||HD 121901||210.073||-61.481||6.800||6.475||6.286||0.325|
|Comp 5||HIP 66904||205.669||-61.738||7.077||6.864||6.744||0.213|
|Comp 6||HD 118978||205.505||-58.787||5.344||5.375||5.382||-0.031|
Several variable or suspected variable stars are included due to the lack of a sufficient number of bright non-variable stars:
- Check star is the suspected variable NSV 19931 with amplitude 0.03 mag in V.
- Comp 2 is V0883 Cen, an eclipsing binary with period 35.44735 days and amplitude 0.22 mag in V. One component has intrinsic variability of <0.01 mag in V over a period of 55.2 days.
- Comp 3 is the suspected variable NSV 6544 with amplitude 0.05 mag in V.
- Comp 6 is the suspected variable NSV 19920 with amplitude 0.03 mag in V.
As the nova fades new Comp and Check stars will be selected. The finder chart and data table will be updated as necessary.
Observers are asked to average at least three observations and report the mean and standard deviation using the format shown in the DSLR Observation Report Excel file. Extended time series are encouraged.
Click on the image below to see a larger version.
User Loaded Data
Mt John University Observatory Data
This data was recorded by Ed Budding from Mt John University Observatory and reduced by Roger Butland. Authors using this data are asked to acknowledge Prof. Edwin Budding & Roger Butland as well as Mt John University Observatory, operated by the Department of Physics & Astronomy, University of Canterbury.
The following links provide relevant information about this event:
- Link to AAVSO LCG (plot since 01/12/2013)
- Link to AAVSO VSX
- Link to AAVSO VSP
- VSS Google Group discussions:
- Spectra discussions @ ARAS
- Carl Knight’s blog (includes several re V1369)