18007( 2) - 15-Aug-2025 16:56:59 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18007 Version: 2 Check-in Time: 15-Aug-2025 16:56:59 STScI Edit Number: 0 Title Spectroscopy of the complex core of VY Canis Majoris ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nathan Smith University of Arizona Y CoI: Dr. Emma Beasor Liverpool John Moores University N CoI: Dr. Laird Close University of Arizona N ------------------------------------------------------------------------------------ Abstract VY Canis Majoris (VY CMa) is the most luminous, largest, and presumably the initially most massive red supergiant (RSG) known. It is surrounded by a spectacular asymmetric nebula that was imaged by HST over 20 years ago, and shows a complex array of knots, arcs, and large-scale axisymmetric structure. It is a key object for understanding the extreme mass loss of the most massive RSGs and a benchmark for progenitors of SNe that interact with dense circumstellar material. Spectra reveal a range of outflow velocities in these structures that are faster than typical RSG winds, suggesting blasts of uneven mass-loss episodes over the past 1000 yr. The origin of this instability is not known, but it is usually attributed to either magnetic/convective instability near the Eddington limit, or to binary interaction with an unseen companion star. Although the central source in the nebula appeared unresolved in the earlier HST/WFPC2 imaging, a recent ground-based extreme-AO image has revealed that the central core of the nebula is not a point source. Instead, the core seems to be bisected by a dark obscuring lane (a disk?), and a fainter point source (a companion star?) is resolved at about 120 mas from the core. These features would have been just at the edge of the resolution limit in dithered WFPC2 images. We propose to obtain STIS spectra of the core of VY CMa in order to (1) record the spectrum of the fainter companion candidate, to see if it is reflected RSG light or a companion star, and (2) obtain the spectrum across the central obscuring lane to determine if it is molecular/dust obscuration and estimate its column density. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program will use STIS with a 0.1 arcsec slit width to obtain spectra of the central star in VY CMa, as well as a candidate companion star located about 120mas from the star. Both with be observed in low and medium resolution settings (G750L and G750M). ------------------------------------------------------------------------------------ 18007( 2) - 15-Aug-2025 16:56:59 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-VY-CMA EXT-STAR, M V-IV RA=07H22M58.3231S +/- 0.1", J2000 V = 8.691 DEC=-25D46'3.16" +/- 0.1" Reference Frame: ICRS Extended: YES Comments: V magnitude is variable. 8.9 is the magniutude of the star plus scattered light in the iner nebula. Central star is actually fainter than this. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 -1.9580296888911729E-4 0.002232 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18007( 2) - 15-Aug-2025 16:56:59 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.2 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18007( 2) - 15-Aug-2025 16:56:59 - [ 4] Visit: 01 (Objects A and B) Visit Requirements: ORIENT 313D TO 317 D On Hold Comments: Additional Comments: First obtain spectrum of central star (Object A; shorter exposures) with STIS slit oriented roughly east-west, and then offset 0.12 arcsec to north to obtain spectrum of Object B (longer exposures). 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 V-VY-CMA STIS/CCD ACQ F25ND3 MIRROR 1 0.2 S (0.2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-VY-CMA STIS/CCD ACCUM 52X0.1 G750L 7751 WAVECAL=NO, CR-SPLIT=NO 1 30 S (60 PATTERN 1 2 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-VY-CMA STIS/CCD ACCUM 52X0.1 G750L 7751 WAVECAL=NO, CR-SPLIT=NO 1 120 S (240 POS TARG 0.13, null; S) PATTERN 1 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 V-VY-CMA STIS/CCD ACCUM 52X0.1 G750M 7795 WAVECAL=NO, CR-SPLIT=NO 1 120 S (240 PATTERN 1 4 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 V-VY-CMA STIS/CCD ACCUM 52X0.1 G750M 7795 WAVECAL=NO, CR-SPLIT=NO 1 479 S (958 POS TARG 0.13, null; S) PATTERN 1 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-VY-CMA 1 STIS/CCD ACQ F25ND3 MIRROR none none none none 1 N/A V-VY-CMA 2 STIS/CCD ACCUM 52X0.1 G750L 7751 1 none none none 1 N/A V-VY-CMA 2 STIS/CCD ACCUM 52X0.1 G750L 7751 2 none none none 1 N/A V-VY-CMA 3 STIS/CCD ACCUM 52X0.1 G750L 7751 1 none none none 1 N/A V-VY-CMA 3 STIS/CCD ACCUM 52X0.1 G750L 7751 2 none none none 1 N/A V-VY-CMA 4 STIS/CCD ACCUM 52X0.1 G750M 7795 1 none none none 1 N/A V-VY-CMA 4 STIS/CCD ACCUM 52X0.1 G750M 7795 2 none none none 1 N/A V-VY-CMA 5 STIS/CCD ACCUM 52X0.1 G750M 7795 1 none none none 1 N/A V-VY-CMA 5 STIS/CCD ACCUM 52X0.1 G750M 7795 2 none none none 1 N/A 18007( 2) - 15-Aug-2025 16:56:59 - [ 5] Summary Form for Proposal 18007 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.1, F25ND3 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 313D TO 317 D, PATTERN 1 2, PATTERN 1 3, PATTERN 1 4, PATTERN 1 5, POS TARG 0.13, null ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G750L, G750M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-VY-CMA ------------------------------------------------------------------------------------------------------------------------------------