For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present.0Assigned ID: 6542
----- Attempting Submission 1 (Thu Apr 10 17:19:10 GMT 2025) -----
HST Phase I Proposal 6542 successfully submitted.
Receipt: # 6542-1We will use the default LP6 with G160M, which requires no justification.INEFFICIENT ORDERING OF FP-POS POSITIONS
For the best data quality, it is generally required to use all four FP-POS positions at a given COS cenwave (or 2 positions for certain exception cases). See extended explanation in the diagnostic browser.
For the best data quality, it is generally required to use all four FP-POS positions at a given COS cenwave (or 2 positions for certain exception cases). See extended explanation in the diagnostic browser.
For the best data quality, it is generally required to use all four FP-POS positions at a given COS cenwave (or 2 positions for certain exception cases). See extended explanation in the diagnostic browser.I messaged my CS for some advice on COS FP-POS execution, so the observing details may need to be revised later.
01/29/2026- CS for STIS observation: Recommended removing ACQ/PEAK from STIS observations with the requested slit, so that has been removed from the observing plan.1920825246----- Attempting Submission 1 (Thu Aug 14 19:04:21 GMT 2025) -----
HST Phase II Proposal 18092 successfully submitted.
Receipt: # 18092-1
----- Attempting Submission 2 (Thu Jan 29 18:48:04 GMT 2026) -----Messaged CS regarding FP-POS recommendations. Observing strategy may change and eliminate remaining errors.Connecting stellar mergers to peculiar stellar behavior with a Rosetta Stone young merger remnantBinary and multi-star systems make up over 1/3 of the star systems in the Galaxy, with some ending with the complete engulfment of one star by another. The latter process is observed only in a few cases because the engulfment happens quickly, but is a likely outcome for a sizable fraction of the all binary systems. Current models of stellar mergers suggest that the merger remnant puffs up to large radius, carries additional angular momentum, and leadis to the formation of a convective zone and active dynamon. Over time, the star contracts, spinning up further and leading to the formation of a rapidly rotating star with significant stellar activity. The mergence of a convective zone may lead to the generation of a strong magnetic field. Magnetic fields may drive
magnetorotational accretion of surrounding material, slow down rotation via magnetic breaking, and power jets -- all of which transport angular momentum from the merger remnant. Therefore, it remains unclear whether these systems evolve to become a rapid rotators.
TYC 2597-735-1 was recently identified as a stellar merger remnant, whose collision occurred a few thousand years ago. It sits in an observationally rare category - one whose merger was old enough to emerge from its dusty aftermath, yet recent enough to still exhibit signs of a stellar merger. Our program will use HST/COS FUV and HST/STIS NUV spectroscopy to obtain a complete UV (1150 - 3000 {\AA}) spectrum at low- to moderate-resolution of TYC 2597 to disentangle the physical processes (magnetic activity, accretion, and outflows), probed using UV hot gas lines, warm circumstellar H2 features, and the UV accretion continuum, that shape its final state.We request a Small GO program, comprised of 14 orbits total, to observe TYC 2597-735-1 (TYC 2597) using COS G130M(1291), G160M(1577), and STIS G230L spectroscopic modes. We request the following exposure times and orbits, which assume 2250 seconds of science exposure and 740 seconds of slew/settle time per orbit:
COS G130M, CENWAVE=1291: 5 orbits
COS G160M, CENWAVE=1577: 8 orbits
STIS G230L, NUV-MAMA, 52'' x 0.2'': 1 orbit
HST/COS exposure times are calculated using signal-to-noise (SN) of 10 for hot gas chromospheric and accretion lines (e.g, C III, C IV, Si IV) and the brightest H2 fluorescence lines (based on the expected Lya flux from TYC 2597, estimated from its Ha flux). The COS grating positions were chosen to maximize coverage of hot gas accretion lines (C III 1175, LyA 1216 (wings), Si IV 1402, C IV 1548, He II 1640) and warm molecular disk (H2 Lyman-Werner electronic emission (1160 - 1620 Angstroms).
HST/STIS exposure times were calculated by assuming a SN = 20 at 2000 Angstroms, the lowest flux region in TYC 2597's NUV spectrum. We require high SN across the NUV-optical bandpass to accurately model the accretion shock continuum and mass accretion rates. The STIS NUV observations (1800 - 3000 Angstroms) provides simultaneous access to the peak accretion shock continuum emission through where the star's photospheric continuum begins to dominate the continuum emission.
Exposure times were estimated for each instrument using a normalized UV spectrum of a pre-main sequence star (RECX-11) and re-scaling the spectrum to TYC 2597's FUV magnitude (20.5 AB). TYC 2597 has a distance of 1.93 kpc (GaiaDR2), an effective temperature of T = 5850 K, and an observed radial velocity ~8.7 km/s. TYC 2597 is at a high galactic latitude (+39.4 degrees above the galactic plane). IRSA extinction maps show E(B-V) = 0.04 +/- 0.02 for a 3' radius around TYC, strongly suggesting that absorption by interstellar dust and hydrogen will not play a significant role in attenuating our FUV observations (A(V) ~ 0.13, assuming R(V) = 3.1).Dr. Keri Hoadley (PI) is an expert in molecular fluorescence and UV spectroscopy. She has both built a high resolution far-UV spectrograph, which has flown aboard several sounding rocket missions (Hoadley et al. 2014, 2016, 2020), and written several papers on the data reduction and analysis of warm molecular regions in planet forming disks using HST-COS spectra (Hoadley et al. 2015, 2017, 2020a). She led the discovery paper of the Blue Ring Nebula around TYC 2597-735-1 and its interpretation as a recent stellar merger (Hoadley et al., 2020b).
Drs. Moritz Guenther and Christian Schneider are experts in both UV and X-ray spectroscopic diagnostics in pre-main sequence accretion disks. They bring extensive knowledge of accretion diagnostic interpretation and analysis techniques that compliment the scope of this program. Dr. Max Guenther is an expert in stellar astrophysics with a specialty in low mass stars with convective regions, and his expertise will be invaluable when interpreting the UV hot gas features we observe from TYC 2597-735-1. Dr. Nicole Arulanantham specializes in UV molecular absorption and emission line characterization and modeling for planet-forming disk environments.
Prof. Chris Martin (PI, GALEX) and Drs. Don Neill and Mark Seibert were key investigators on the GALEX science team responsible for the discovery of the Blue Ring Nebula around TYC 2597-735-1 and for follow-up ground observations that led to its discovery as a recent (~1,000 year) stellar merger remnant. They bring their expertise on the current suite of data we have the BRN and its central star to interpreting the new UV spectra we will obtain with COS and STIS.
Prof. Brian Metzger and Dr. Ken Shen provide analytic and theoretical perspective to this program, both having been key to unraveling the origins of the Blue Ring Nebula and its relationship to TYC 2597-735-1. Both intuitively tie observational evidence to theory and will provide this perspective for future literature published using these novel datasets.Stellar Physics and Stellar Types6falsetruefalsefalsefalsefalseSUPPORTEDSTARACCRETION DISKCIRCUMSTELLAR MATTERF0-F2F3-F9WINDNOJ2000J200020.5 (FUV), 15.4 (NUV), 11.71 (B), 10.95 (G), 9.98 (J)COS/FUVSpectroscopicNoNoG130M1291COS/FUVSpectroscopicNoNoG160M1577STIS/NUV-MAMASpectroscopicNoNoG230L2376/private/var/folders/yw/w_0k4q7s2679ght1rhb5d25h0000gp/T/OPVisit10770809533484308767.xmlThe scheduling data was generated by CASM 33.1.CASM was run in Phase II mode.Orbit 1 (out of 1)(Tic-Visit
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