Cataclysmic Variable

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UU Aql Dwarf Nova

2022-08-07T18:03:48+00:0022 July 2022|Cataclysmic Variable, Dwarf Nova, News, Variable Star|

X28087AF chart

Following the AAVSO campaign to observe some Dwarf Novae along with Hubble. The main aim is to determine when the star is faint enough for Hubble to observe it – to avoid damage to its sensors!

Alert Notice 758: Monitoring requested for 11 dwarf novae in support of HST observations in 2021-2022

Has had a recent outburst and my latest two measurements show it as V mag. 16.9 on 2022-07-11 and then on 2022-07-20 a V mag. of 12.3. Quite an outburst. Seems to happen every 2 months.

Photometry using ASTAP, plot from AAVSO VStar.

UPDATE: 2022-07-31 now very faint down at mag. 17 and on its base magnitude.

UU Aql 2022-07-11 Mag. 16.94 +- 0.09 / 2022-07-20 Mag. 12.33 +- 0.01

UU Aql 2022-07-11 / 2022-07-20

Mag. 16.94 +- 0.09 / Mag. 12.33 +- 0.01

Object IDUU Aql
Details2022-07-11 23:49 UT
2022-07-20 23:04 UT
Telescope250mm f4.8 Newtonian, MPCC
CameraAtik 460EX @-10°C
FiltersPhotometric V
Exposure(s)3 x 180s
2 x 180s
d,f,b
CaptureNINA
ProcessingASTAP, VStar

Dwarf Nova illustration

Credit: NASA and L. Hustak (STScI)

Current theory suggests that dwarf novae result from instability in the accretion disk, when gas in the disk reaches a critical temperature that causes a change in viscosity, resulting in a temporary increase in mass flow through the disc, which heats the whole disc and hence increases its luminosity. The mass transfer from the donor star is less than this increased flow through the disc, so the disc will eventually drop back below the critical temperature and revert to a cooler, duller mode. Wikipedia

DO Dra

2022-07-22T11:30:53+00:0012 May 2022|Cataclysmic Variable, Intermediate Polar, News, Variable Star|

AAVSO “Alert Notice 753: Monitoring requested for seven intermediate polars” – DO Dra (also known as YY Dra) is on the list, it’s circumpolar and easy from here.

“Photometry (V, CV) of the targets in the table below is requested. DSLR green and visual observations are welcome to supplement the light curves. The cadence requested is every other night, as weather permits, and “about one hour of coverage per night (enough to catch a few spin cycles of the white dwarf). If a source is found to be in a low state, then we request longer coverage and nightly cadence. SNR>>10 is ideal…”

Photometry (V, CV) of the targets in the table below is requested. DSLR green and visual observations are welcome to supplement the light curves. The cadence requested is every other night, as weather permits, and “about one hour of coverage per night (enough to catch a few spin cycles of the white dwarf). If a source is found to be in a low state, then we request longer coverage and nightly cadence. SNR>>10 is ideal…”

Covington adds: “These systems show periodic variability on the spin period of the WD, usually on order of ~10 minutes. So, shorter exposure times are needed so the spin variability isn’t washed out. Previous AAVSO observations of these sources have had exposure times <60s, which is ideal. Also, accurate time tagging of the observations is required, so we can measure periodicities!”

Thought I’d give it a go for 1 hour. Uploaded to AAVSO and BAA databases.

Object IDDO Dra
Typical/high state mag. 15.0 – 15.5 V
Range: 10.0 – 17.2 V
Details23:00 – 23:59 UT
Telescope250mm f4.8 Newtonian
CameraAtik 460ex @-10°C
FiltersV photometric
Exposure(s)70 x 60s
dfb
CaptureNINA
ProcessingASTAP

An Intermediate Polar (also called a DQ Herculis Star) is a type of cataclysmic variable binary star system with a white dwarf and a cool main-sequence secondary star. In most cataclysmic variables, matter from the companion star is gravitationally stripped by the compact star and forms an accretion disk around it. In intermediate polar systems, the same general scenario applies except that the inner disk is disrupted by the magnetic field of the white dwarf.

The name “intermediate polar” is derived from the strength of the white dwarf’s magnetic field, which is between that of non-magnetic cataclysmic variable systems and strongly magnetic systems. Non-magnetic systems exhibit full accretion disks, while strongly magnetic systems (called polars or AM Herculis systems) exhibit only accretion streams which directly impact the white dwarf’s magnetosphere.

Wikipedia