MBCAA Observatory

KU Her: a slow irregular variable

Observed: 12, 13, 14, 15, 19 July, 5, 18 Aug, 5, 6, 12, 15, 19, 20 Sept, 2, 4, 13, 14, 15, 16, 18 Oct 2007

Michel Bonnardeau
25 Sept 2007
Revised 27 Sept 2007
Revised 29 Sept 2007 ("weighted" transformation coefficients)
Updated 5 Oct 2007 (more observations)
Revised 10 Oct 2007 (B transformed from TbTbv instead of Tbv, I transformed from R instead of V)
Updated 17, 20 Oct 2007 (more observations)


Multicolor photometry of this irregular variable star are presented.


KU Her is classified as a "slow irregular variable" (LB type).

The AAVSO issued the Alert Notice 351 (June 8, 2007) to start a campaign of observations on ASAS1826+12 (a Cepheid in an eclipsing binary system) and, as a "by-product", of KU Her in the same field.


The observations were carried out with a 203mm f/6.3 SC telescope, BVRcIc Johnson-Cousins filters (from Schuler) in a filter wheel and a SBIG ST7E camera (KAF401E CCD). Each exposure is 200s long with one exposure/measurement (no stack).

For the photometry, the comparison star and the check star recommended by the AAVSO are used. They are:

(comp is AAVSO chart 070925 star 119).


The measured b,v magnitudes may be transformed for the instrument response. The transformed B,V magnitudes are then:

V = v + TvTbv*[(b-v)-(Bc-Vc)]
B = b + TbTbv*[(b-v)-(Bc-Vc)]

Bc,Vc are the magnitudes of the comparison star. The transformation coefficients were measured HERE; they are:
TbTbv = 0.002 +/- 0.027
TvTbv = -0.025 +/- 0.015

The transformed R magnitudes (Rc filter) are computed from the observed r magnitudes the same way:

R = r + TrTvr*[(v-r)-(Vc-Rc)]

with the transformation coefficient:
TrTvr = -0.134 +/- 0.017

And the transformed I magnitudes (Ic filter) from the observed i magnitudes:
I = i + TiTri*[(r-i)-(Rc-Ic)]

with the transformation coefficient:
TiTri = 0.022 +/- 0.011

The transformed light curves:

Blue: the B measurements, shifted by -1.0 mag;
Green: the V measurements;
Red: the Rc measurements, shifted by +1.0 mag;
Brown: the Ic measurements, shifted by +2.5 mag.
The error bars are computed from +/- the 1-sigma statistical uncertainties and the 1-standard deviations on the transformation coefficients.

The check star measurements are reported in the ASAS1826+12 page.

Color variations

The (transformed) B, Rc, Ic magnitudes as a function of V:

Blue: B magnitudes; Red: Rc magnitudes shifted by +2.2 mag; Brown: Ic magnitudes shifted by +3.0 mag.

As the star becomes brighter in V, it becomes brighter in B at about the same rate (slope +1.00), in Rc at slower rate (slope +0.49), and stays almost constant in Ic (slope +0.07).

Technical notes

Telescope and camera configuration.

Computer and software configuration.

Transformations for differential photometry.

Transformation coefficients: B, V measurements.

Transformation coefficients: V, Rc measurements.

Transformation coefficients: Rc, Ic measurements.

Astronomical notes

Pulsating stars and its links.

ASAS1826+12, a Cepheid in an eclipsing binary system, in the field of view of KU Her.

Site map


Copyright notice

Observations submitted to the AAVSO International Database, observer BZU.
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