Alert Notice 526: Monitoring of LS IV -14 116 in support of upcoming satellite observations

August 20, 2015Prof. Simon Jeffery (Armagh Observatory; Trinity College Dublin) has requested photometric monitoring of the pulsating helium and zirconium-rich hot subdwarf LS IV -14 116 in support of upcoming HST and VLT/UVES spectroscopy. AAVSO observations will supplement photometry due to be obtained with the SAAO 1.0-m and IAC 0.8-m telescopes from 18 August to 2 September 2015. Photometry is requested beginning immediately through 2 September.

LS IV -14 116 is magnitude V=13.0 and B=12.6. Prof. Jeffery writes: "The star shows at least 5 independent pulsation frequencies. The objective of these observations is to resolve the frequencies, to measure their amplitudes, and also to measure the amplitude of any colour variations, so as to set the high-resolution spectroscopy and ultraviolet spectrophotometry into context.

"Requirements are:

i) at least one of Johnson B and V filters (both if available, cycled BVBVB..., and/or  BVRBVR... or BVIBVI...)

ii) 10,000 target counts per frame (for LS IV-14 116, unless bright comparison is saturated and no other good comparisons in field). The 10,000 counts requirement is indicative rather than a minimum, and exposures of up to 100 s are acceptable, so long as the overall cadence provides a data point in each filter every 300 s (5 minutes) or less. The shortest period exhibited by the star is 1950 s, which we would like to sample well.  

iii) exposures times 60 seconds or less (per filter)

iv) timestamps on image frames to be precise and regularly checked against GPS or other external clock

v) minimum useful runs: 2 hours; data obtained over long runs and several nights is preferred

vi) useful dates: 19 August to 2 September

"...If AAVSO observers prefer not to exercise their filter wheels all night, then continuous photometry in just the B-band would be acceptable. I am conscious that many filter wheels for the commercial market are not very robust (we have one in Armagh!). We can deduce the colour amplitudes from fewer sites, but refining the window function for the B data would be really good."

For some general background on this fascinating type of star, see:

Coordinates:  RA 20 57 38.88   Dec -14 25 44.0  (J2000)

Finder charts with comparison stars for LS IV -14 116 may be created using the AAVSO Variable Star Plotter (VSP, A photometry table is also available via VSP.

For those using CCD chips with a small field of view, Prof. Jeffery requests the comparison stars TYC 5782-1367-1 and 2MASS J20574148-1426122 (labeled 112 and 147, respectively, in the AAVSO sequence). However, observers whose CCD chip has a larger field of view are urged to use comparison stars other than the 147 because that star is very red and the target is blue. Also, observers using the 112 in particular are cautioned to beware of saturating this comp star.

Please report observations to the AAVSO International Database using WebObs and the name "LS IV -14 116". Be careful to include all the spaces in the name as shown.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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