VARIABLE STARS

2014 October 02.

"MIRA" Class Variables: Observation Programme:

We shall be featuring observations on Mira class variables. A list of stars currently being monitored is given below.

2014 October 01:

Two stars, one close to minimum the other close to maximum, namely U Cyg. and S Corona Bor. The former is as red as a beetroot, the other hardly tinged at all! (See table for more information on luminosity range and position.) In both cases the featured star appears at the centre of the field.

U Cygni. 2014 October 01, 20h 13m UT. An 8 sec. exposure with Tokina 300mm f5.6  (f/2.8 with 2x converter) D800 SLR, ISO 2000. Field diameter a little under 2°. 
The star close by (right) is TYC 3576-2095-1, mag. 7.87 Spectral class: G0. 

S Corona Bor. 2014 October 01, 19h 53m UT. A 10 sec. exposure with Tokina 300mm f5.6  (f/2.8 with 2x converter) D800 SLR, ISO 2000. Field diameter a little under 2°. Two other variables are in the field, U Cor. Bor. (mag. 7.66 - 8.79  and UU Cor Bor. (mag. 8.59 - 8.64.). Stars to 16 magnitude visible on high resolution images despite presence of Moon.

Data for Moon at 19h 53m UT:

Right ascension: 18h 36m
Declination: -18° 54'
Constellation: Sagittarius
Altitude: 8° 49'
Azimuth: 206° 26'
Phase: 50.3%

2014 September 29:

The month of September has proved a non-starter from an observational point of view, by which we mean there have been very few clear periods at night. Usually we expect to get at least four or five decent nights in early autumn before things go down hill for the rest of the autumn and winter itself!

The night of September 29/30 offered around two hours of usable clarity. Details below for some aspects of the work undertaken.

Galaxies Galore and More!

In this photograph (field 1.8˚ x 2.7˚) there are at least 20 galaxies visible at low resolution, and well over that number on the original high resolution image.

The image is one of a series looking at Mira class variable stars: super-giant M spectral class stars sometimes referred to as pulsating variables and taking their name from Mira (omicron Ceti). These stars are characterised by having long, irregular periods between maximum and minimum over a wide luminosity range.

This field looks specifically at S Pegasi, readily identified at the centre of the cropped image (1.1˚ dia. approx. : note the distinct reddish colouration).

(Left click to enlarge this image.)

Observational data: 2014 September 29, 22h 09m. A 30 sec. exposure, Nikkor 500mm f/4, D300 SLR ISO 2000. (Stars to magnitude 16.5 visible on high resolution image.) (Left click to enlarge this image.)

Data for S Pegasi

Maximum magnitude: 6.9
Minimum magnitude: 13.8
Range in luminosity: 600+
Type of variability: M
Spectral type: M5E-M8.5E 
Distance: 1059 +/- 423 light years

Data for Mira:

Maximum magnitude: 2.0
Minimum magnitude: 10.1
Range in luminosity: 1,500 approx.
Type of variability: M
Spectral class: M5e-M9e 
Distance: 419 +/- 51 light years