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AAVSO Alert Notice 526
August 20, 2015
Monitoring of LS IV -14 116 in support of upcomingsatellite observations
Prof. Simon Jeffery (Armagh Observatory; Trinity CollegeDublin) has requested photometric monitoring of the pulsating helium andzirconium-rich hot subdwarf LS IV -14 116 in support of upcoming HST andVLT/UVES spectroscopy. AAVSO observations will supplement photometry due to beobtained with the SAAO 1.0-m and IAC 0.8-m telescopes from 18 August to 2September 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 pulsationfrequencies. The objective of these observations is to resolve the frequencies,to measure their amplitudes, and also to measure the amplitude of any colourvariations, so as to set the high-resolution spectroscopy and ultravioletspectrophotometry into context.
"Requirements are:
i) at least one of Johnson B and V filters (both ifavailable, 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 aminimum, and exposures of up to 100 s are acceptable, so long as the overallcadence 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 tosample well.
iii) exposures times 60 seconds or less (per filter)
iv) timestamps on image frames to be precise andregularly checked against GPS or other external clock
v) minimum useful runs: 2 hours; data obtained over longruns and several nights is preferred
vi) useful dates: 19 August to 2 September
"...If AAVSO observers prefer not to exercise theirfilter wheels all night, then continuous photometry in just the B-band would beacceptable. I am conscious that many filter wheels for the commercial marketare not very robust (we have one in Armagh!). We can deduce the colouramplitudes from fewer sites, but refining the window function for the B datawould be really good."
For some general background on this fascinating type ofstar, see:
Coordinates: RA 2057 38.88 Dec -14 25 44.0 (J2000)
Finder charts with comparison stars for LS IV -14 116 maybe created using the AAVSO Variable Star Plotter (VSP, https://www.aavso.org/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 2MASSJ20574148-1426122 (labeled 112 and 147, respectively, in the AAVSO sequence).However, observers whose CCD chip has a larger field of view are urged to usecomparison stars other than the 147 because that star is very red and thetarget is blue. Also, observers using the 112 in particular are cautioned tobeware of saturating this comp star.
Please report observations to the AAVSO InternationalDatabase using WebObs and the name "LS IV -14 116". Be careful toinclude all the spaces in the name as shown.
This AAVSO Alert Notice was compiled by Elizabeth O.Waagen.
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發表於 2015-8-21 08:29:58