14736( 2) - 29-Jun-2016 19:17:57 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14736 Version: 2 Check-in Time: 29-Jun-2016 19:17:57 STScI Edit Number: 0 Title Connecting Variability and Metals in White Dwarfs ------------------------------------------------------------------------------------ Type Cycle GO 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Mukremin Kilic University of Oklahoma Norman Campus Y CoI: Dr. Alexandros Gianninas University of Oklahoma Norman Campus N CoI: Dr. Patrick Dufour Universite de Montreal N CoI: Dr. Warren R. Brown Smithsonian Institution Astrophysical N Observatory CoI: Keaton Bell University of Texas at Austin N ------------------------------------------------------------------------------------ Abstract The Kepler and K2 missions have revealed that about half of the observed white dwarfs with sufficient signal-to-noise ratio light curves have low-level photometric variations at hour to day timescales. Potential explanations for the observed variability include the relativistic beaming effect, ellipsodial variations, eclipses, and reflection off of giant planets in close orbits. However, these are all rare events. Roughly 10% of white dwarfs are magnetic, and magnetic fields can explain part of this puzzle. However, the high incidence (50%) of variability is currently unexplained. HST COS spectroscopy of nearby white dwarfs show that about half of them have metals on their surface. Hence, we propose that the observed variability is due to the rotation of the star coupled with an inhomogeneous surface distribution of accreted metals. We have recently discovered an ideal system to test this hypothesis. J1529 is an apparently non-magnetic white dwarf that shows 5.9% photometric dips in the optical every 38 min. We propose to obtain COS TIME-TAG spectroscopy of J1529 over 4 orbits to search for surface abundance differences throughout the orbit and look for the flux redistribution effect in the optical. These observations will confirm or rule out the idea that inhomogeneous metal accretion on white dwarfs can explain the high incidence of variability. We predict that the LSST will identify ~100, 000 variable white dwarfs. Hence, understanding the source of variability in white dwarfs has implications for the current and future transient surveys. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use COS/TIME-TAG mode to obtain G230L spectra (with the nominal wavelength setting of 2635 Angstrom) of a white dwarf that shows photometric dips every 38 minutes. We think that the source of these dips is surface inhomogeneities of accreted metals. Our goals is to get a S/N=20 spectrum to search for metal lines within and outside of the photometric dips. We divide each orbit into 2 sub-exposures using FP-POS 1, 2, 3, and 4 for the orbits 1, 2, 3, and 4, respectively. We will obtain simultaneous ground-based, optical photometry from McDonald and APO telescopes. Hence, we will need to know the HST scheduled dates as soon as 14736( 2) - 29-Jun-2016 19:17:57 - [ 2] possible so that we can plan for the ground-based observations. ------------------------------------------------------------------------------------ 14736( 2) - 29-Jun-2016 19:17:57 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J1529+2928 STAR, DA RA=15H29M34.9809S +/- 0.1", J2000 V = 17.47 u=17.77 AB mag DEC=+29D28'1.87" +/- 0.1" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2003.47 -0.005771094093120665 -0.006913108 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 14736( 2) - 29-Jun-2016 19:17:57 - [ 4] Visit: 01 (J1529) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 J1529+2928 COS/NUV ACQ/IMA PSA MIRRORA 1 7 S (7 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=1, 1 1240 S G FLASH=YES see below (1251 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=1, 1 1240 S G FLASH=YES see below (1252 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=2, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=2, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=3, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=3, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=4, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 J1529+2928 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1625, FP-POS=4, 1 1420 S G FLASH=YES see below (1424 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ 14736( 2) - 29-Jun-2016 19:17:57 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ J1529+2928 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J1529+2928 2 COS/NUV TIME-TA PSA G230L 2635 none none none none 1 1251.0 S G J1529+2928 3 COS/NUV TIME-TA PSA G230L 2635 none none none none 1 1252.0 S G J1529+2928 4 COS/NUV TIME-TA PSA G230L 2635 none none none none 2 1424.0 S G J1529+2928 5 COS/NUV TIME-TA PSA G230L 2635 none none none none 2 1424.0 S G J1529+2928 6 COS/NUV TIME-TA PSA G230L 2635 none none none none 3 1424.0 S G J1529+2928 7 COS/NUV TIME-TA PSA G230L 2635 none none none none 3 1424.0 S G J1529+2928 8 COS/NUV TIME-TA PSA G230L 2635 none none none none 4 1424.0 S G J1529+2928 9 COS/NUV TIME-TA PSA G230L 2635 none none none none 4 1424.0 S G 14736( 2) - 29-Jun-2016 19:17:57 - [ 6] Summary Form for Proposal 14736 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1625, FLASH=YES, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names J1529+2928 ------------------------------------------------------------------------------------------------------------------------------------