0 Assigned ID: 7263 ----- Attempting Submission 1 (Thu Apr 16 02:27:09 GMT 2026) ----- 0 ----- Attempting Submission 1 (Fri Aug 14 20:33:09 GMT 2026) ----- Stellar mass loss is a ubiquitous property of stars, as are planets and circumstellar dusty debris disks. In the case of our own star, the Sun, the unique properties of its particle wind shape the structure of our debris disks, dictate the thermal and chemical structure of planetary atmospheres, and ultimately push against the confining plasma of our surrounding interstellar medium, producing the heliosphere. The detection of astrospheres, the result of the relatively weak winds of solar-like, cool, stars can be made with high-resolution spectra of Lyman-alpha, a unique capability of HST. Charge exchange in the interaction zone of stellar winds with their surrounding interstellar medium produces detectable HI Lyman-alpha absorption, where the amount of absorption allows for a determination of the mass loss rate. A well-known nearby young debris disk, HD61005, (also known as The Moth due to the captivating morphology of the scattered light of its disk) was recently discovered to have extended X-ray emission that is associated with its astrosphere. We propose UV spectroscopy in order measure Lyman-alpha profile and detect or constrain the astrospheric signature of hot, excess hydrogen at the interface of the astrosphere and local interstellar medium. These observations would provide a comprehensive view of HD61005's astrosphere and provide a valuable model for our own Sun's heliosphere early in its main-sequence lifetime. Desired Spectral Coverage and Resolution: The high spectral resolution capabilities of STIS are necessary to adequately model potentially blended LISM absorption line profiles and resolve the critical DI line. We propose to use the E230H (R ~ 110,000) grating, in the 2574-2851 A wavelength range, which encompasses MgII h & k near 2800 A and FeII at 2600 A to resolve the velocity structure of the ISM along the line of sight. Because the hydrogen at the astrospheric interface is hot (T ~ 100,000 K), it has a broad absorption profile, and does not necessarily require the highest spectral resolution. To maximize the S/N we plan to use the E140M setting. Desired Signal-to-Noise and Exposure Times: Estimating the S/N for our planned spectra requires first estimating the expected Lyman-alpha and MgII fluxes of HD61005. Chromospheric line fluxes (such as MgII and Lyman-alpha) are correlated to X-ray fluxes. Lyman-alpha spectra of similar stars are used as the comparison stars for our purposes here, scaled by their X-ray flux. After acquisition, peakup, and observational overhead are considered, we expect at least 28 minutes to be available in the first orbit for the E230H exposure. We expect a S/N of ~25 per resolution element at MgII. We expect at least 41 minutes of exposure time to be available in the second orbit for the E140M exposure, and 48 minutes in subsequent orbits. For 4 orbits we expect to reach S/N > 15 in the Lyman-alpha profile, which is sufficient to detect astrospheric absorption. Brightness Limits: HD61005 has been previously observed at medium resolution (E230M) which is insufficient to detect and model interstellar or circumstellar absorption but provides an excellent basis to evaluate the brightness limit at MgII. The global count rate is only 1,900 counts per second, about 100 times less than the global brightness limit. The two emission lines of interest in the HST observations (Lyman-alpha and MgII) are also the brightest, and the procedure given above for estimating the S/N is also used to test for brightness limit violations. In the strongest lines, the brightest pixel only generates 0.1 counts per second. PI Redfield is a leading expert on the local interstellar medium. He has extensive experience with the spectrographs on HST to observe the interstellar medium, stellar atmospheres, circumstellar disks, and exoplanets. He has published more than 30 papers based on high resolution HST spectra of nearby stars, detailing the physical and morphological structure of the gas and dust in the immediate vicinity of the Sun and the nearest stars. He recently chaired the Space Telescope Science Institute Working Group on Strategic Exoplanet Initiatives with HST and JWST. Co-I Dennerl in an expert in low energy X-ray emission lines, especially those generated by charge exchange. Dr. Dennerl has substantially contributed to the energy calibration of the EPICpn camera onboard XMM-Newton and is providing the energy calibration for eROSITA. He is an author or co-author of 112 refereed papers. Co-I Koutroumpa is an expert of the heliosphere, the Sun's astrosphere, and the solar wind interaction with interstellar neutrals flowing through it, in particular soft X-ray emission from solar wind charge exchange. She has authored or co-authored 56 refereed papers. Co-I Guenther is a member of the Chandra X-ray Center gratings team. He is responsible for MARX, a simulation program that is used to calibrate Chandra and to plan and analyze Chandra observations. He is the team leading for ray tracing for Arcus Probe. His research research focuses on young stars and how the disk and jet interact by looking at the closest star forming regions in our galaxy. He is lead author of 27 refereed papers. He will be responsible work the precision measurements of the PSF. He is an author or co-author of 101 refereed papers. Co-I Linsky has been on science working groups that have successfully proposed, analyzed, and published the first observations from the Far-Ultraviolet Spectroscopic Explorer (FUSE) satellite and three of the spectroscopy instruments on HST: GHRS, STIS, and COS. His work includes studies of the interstellar medium, stellar chromospheres, stellar coronae, and stellar winds. He has authored more than 400 refereed publications. In 2019, he published the book "Host Stars and their Effects on Exoplanet Atmospheres". Co-I Lisse has pioneered the detection and understanding of the charge exchange driven X-ray emission from comets and planets in our solar system using ROSAT, EUVE, XMM, and Chandra. A Chandra observer since Cycle 2 and lead for the Chandra Pluto observations in 2014-2015, he is currently using the observatory to extrapolate solar systems studies to the formation and evolution ofnearby exo-solar systems, e.g. in the 2017 comparative Chandra study of the two very different debris disks found in the young, rocky-planet building, close F-star binary system HD113766, in the 2020 findings of strong stellar-flare-altered circumstellar disk material in the HD145263 system, and in the 2025 imaging study of HD61005's astrosphere. Co-I Wolk is a member of the Chandra X-ray Center and Flight Director of the Chandra X-ray Observatory. He is a member of the Line Emission Mapper (LEM), Athena, AXIS and Arcus Probe science teams as well as the NASA New Great Observatories Science Analysis Group. He is the Author or Co-Author of over 150 refereed papers, about half of which involve Chandra data. Over 20 of these paper deal directly with charge exchange emission. Co-I Wood is the leading expert on UV observations of hydrogen in the heliosphere and astrospheres. He has performed detailed analysis of the Lyman-alpha profile, which is complicated by LISM absorption, the neighboring DI line, heliosphere and astrospheric absorption, and geocoronal emission. In 2004, he wrote a review of astrospheres in Living Reviews in Solar Physics. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false true false false false false false SUPPORTED STAR DISK EMISSION LINE STAR G V-IV NO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18336 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "14-Aug-2026 16:13:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 314624 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18336 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18336 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2607 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18336 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2607 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2987 :pcs-gap 0 ) true 2 0 SNR = 152.6861 Brightest Pixel = 9,707.79 e SNR = 80.0255 Brightest Pixel = 2,855.23 e Global Source Counts = 14,130.055 e SNR = 10.7068 Brightest Pixel = 56.14 e SNR = 13.8863 Brightest Pixel = 94.44 e