Wolf-Rayet stars in the outskirts of M33: unveiling helium-star evolution and feedback at subsolar metallicity

Initial submission 1446151624 Assigned ID: 672 ----- Attempting Submission 1 (Fri Mar 06 19:11:40 GMT 2020) ----- Resubmission with updated ETC links for visit 5 as discussed with the contact scientist Ravi Sankrit, resolving an issue with a bright pixel warning for the TA. (see visit comments for details) -900165567 ----- Attempting Submission 1 (Sun Jun 21 23:40:49 GMT 2020) ----- ----- Attempting Submission 2 (Wed Oct 14 19:33:04 GMT 2020) ----- Wolf-Rayet stars in the outskirts of M33: unveiling helium-star evolution and feedback at subsolar metallicity Massive stars are important drivers of the evolution of galaxies. They shape the structures around them and enrich the interstellar medium with metals due to their strong stellar winds. They ionize their environment and transfer momentum from the UV-dominated radiation field to metals. As the progenitors of heavy black holes, evolved massive stars have become a keystone of modern astrophysics. The masses of their black hole remnants predominantly depend on the wind mass loss of envelope-stripped helium (He) stars. The mass loss of these He-burning stars and its metallicity-dependence mark a crucial, yet poorly constrained astrophysical quantity. He stars with a sufficiently high mass loss appear as Wolf-Rayet (WR) stars, detectable even in unresolved stellar populations and distant galaxies due to their strong emission lines. While the general presence of WR stars is known to be correlated with metallicity, recent studies show that current assumptions in stellar evolution and population models are too simplistic. Thus, a proper empirical determination of WR mass loss as a function of mass and metallicity is necessary to understand the true nature and complex metallicity-dependent behaviour of He star mass loss. The diagnostics to determine the metallicity of He stars can only be obtained from UV spectroscopy. We therefore propose COS UV observations of six WR stars in the outskirts of M33, providing a unique opportunity to study very massive evolved He stars at subsolar metallicity. By anchoring mass loss of WR stars in this crucial environment, our observations will deliver one of the most important ingredients needed for realistic stellar evolution and feedback models. We propose to observe six WR stars in the outskirts of M33 with FUV spectroscopy, aiming at a S/N of 20 at 1310 Angstroem. The spectral observations will be performed with the G140L grating with pass band 770 - 1950. This relatively new setting covers the far UV range in one arm, including even strong emission lines below Lyman alpha. Furthermore, this spectral range contains important wind lines, such as the resonance lines of Civ, Nv, and Ovi which act as crucial indicators in order to determine the correct wind parameters and properly constrain the stellar temperature below the expanding layers. Due to the broad lines, the resolution of the G140L grating is sufficient for our spectral analyses with stellar atmospheres, while a S/N of 20 is required to resolve weaker metal lines, detect absorption troughs, and to constrain the iron abundance. All targets combined, we will require 20 orbits to achieve our science goals. The UV provides a unique chance to establish the iron abundance, which is the main driver of massive star winds. While most targets will show only imprints of Fe VI and higher at wavelengths below 1300 Angstroem, the cooler WN8h target (Romano's star) will provide us with a detailed iron forest down to Fe iv, spanning all over the proposed pass band and acting as a crucial benchmark. Our brightest target has a magnitude of mV = 18.7 and an estimated reddening of E(B-V) = 0.05, bringing the object safely below the brightness limit of the COS detector. This was confirmed by ETC calculations with an atmosphere model spectrum. As an additional layer of security, we also cross-checked this with a much hotter, unreddened 200 kK black body input normalized to mV. We will follow the recommended observing strategy and request that the default wavelength-calibration procedure is applied. The observations shall be performed in TIME-TAG mode and use all four FP-POS positions for each target as recommended to enhance the detector's lifetime. The proposing team consists of experts from both the theoretical and the observational side with several members having long-time HST experience. The CoIs R. Hainich, L. Oskinova, T. Shenar, W-R. Hamann and R. Ignace have extensive experience with HST UV data with more than half a dozen accepted proposals in the last decade. W-R. Hamann, R. Hainich, A. Sander, M. Pritzkuleit, V. Ramaschandran, H. Todt, and T. Shenar have long-time experience with analysing Wolf-Rayet stars and have published various papers about this matter with multiple of them being now a standard reference in the field. L. Oskinova and R. Ignace add further expertise in the field of wind clumping to the team. M. Pritzkuleit led the preliminary analysis of the WR population in M33 to identify the objects most suitable for this proposal. A. Sander, H. Todt, and W.-R. Hamann are lead developers of PoWR, one of the most advanced expanding non-LTE stellar atmosphere code, especially designed to properly cope with the complex winds of hot Wolf-Rayet stars. Moreover, A. Sander and J. Vink are experts in the theoretical modelling and hydrodynamically consistent simulation of radiation-driven winds of hot stars. E.R. Higgins is an expert in stellar evolution modelling, in particular for evolved massive stars. Stellar Physics and Stellar Types Galaxies 6 false false true false false false false SUPPORTED EXT-STAR EMISSION LINE STAR WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinate uncertainties from Gaia DR2 GAIA-DR2-303287470635776000 J2000 J2000 EXT-STAR EMISSION LINE STAR WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinate uncertainties from Gaia DR2 GAIA-DR2-303312480229584384 J2000 J2000 EXT-STAR EMISSION LINE STAR WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinate uncertainties from Gaia DR2 GAIA-DR2-303420335449835392 J2000 J2000 EXT-STAR EMISSION LINE STAR WOLF RAYET WOLF RAYET - WC NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinate uncertainties from Gaia DR2 GAIA-DR2-303375599069698816 J2000 J2000 EXT-STAR EMISSION LINE STAR LUMINOUS BLUE VARIABLE WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinate uncertainties from Gaia DR2 BOT lists the star as a bright object exceeding the local pixel maximum, but this is based on a 16.x magnitude from the early 1990s. In recent years, the star has a more stable magnitude of around 18.7 (see, e.g., the review by Maryeva et al. 2019) NM2011-J013509.73+304157.3 GAIA-DR2-303371991297027328 J2000 J2000 EXT-STAR EMISSION LINE STAR WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates from II/349/ps1 aka Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016) as they are the only ones with precise coordinates. (Too faint for Gaia DR2) PS1 Photometry for g and r agree with the model SED and are in line with Massey and XMM-OM Uncertainties not given in J/AJ/152/62/catalog (Revised LGGS UBVRI photometry of M31 and M33 stars from Massey et al. 2016) but their location is only 0.257 from the PS1 data Correlation with Galex data (J/MNRAS/450/3811/table2) has 0.78 arcsec shift to Neugent+ 2011, but both values should have severe uncertainties. M33WR-206 J2000 J2000 COS/FUV Spectroscopic No No G140L 800 COS/FUV Spectroscopic No No G140L 800 COS/FUV Spectroscopic No No G140L 800 COS/FUV Spectroscopic No No G140L 800 COS/FUV Spectroscopic No No G140L 800 COS/FUV Spectroscopic No No G140L 800 1592779651273 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16170 :visit-id "01" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:47:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 113248 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 57 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "01" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 3 0 1592779652308 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16170 :visit-id "02" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:47:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 113248 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 57 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "02" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "02" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 3 0 1592779653368 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. Automatic exposure time adjustment used to distribute the four FP-POS over two orbits (Tic-Visit :proposal-id 16170 :visit-id "03" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:47:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "03" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2778 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "03" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 2 0 1592779654249 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. Automatic exposure time adjustment used to distribute the four FP-POS over two orbits (Tic-Visit :proposal-id 16170 :visit-id "04" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:47:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 121920 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "04" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 57 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "04" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 350 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 2 0 1592779655110 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16170 :visit-id "05" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:47:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "05" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2784 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 1 0 Update of the the ETC run: COS.ta.1449252 was replaced with COS.ta.1469602 to resolve an artefact occuring in the atmosphere model used for the former run. The artefact lead to a bright pixel warning which no longer occured when the atmosphere model without these issues was used. The new model entering the ETC also takes a recent analysis of the optical spectra into account. The resulting TA time is not affected. Update of the the ETC run: COS.sp.1449254 was replaced with COS.sp.1469604 to resolve an artefact occuring in the atmosphere model used for the former run. The new model also takes a recent analysis of the optical spectra into account. The resulting observation time is not affected. 1592779232228 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. Observation of M33WR 206 is split into 2 visits due to Phase II visit length recommendations Visits 6 and 7 are intended to be added up eventually to get a higher S/N (Tic-Visit :proposal-id 16170 :visit-id "06" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:40:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 148032 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "06" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 57 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "06" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "06" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "06" :orbit-number 4 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 4 0 1150 Wavelength setting as 800 is not available for TA 1592779545704 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. Observation of M33WR 206 split into 2 visits due to Phase II visit length recommendations Visits 6 and 7 are intended to be added up eventually to get a higher S/N (Tic-Visit :proposal-id 16170 :visit-id "07" :proposal-version -1 :trans-version "20200518" :date "21-Jun-2020 23:45:45.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 174160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16170 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16170 :visit-id "07" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2787 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "07" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "07" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "07" :orbit-number 4 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16170 :visit-id "07" :orbit-number 5 :pcs-time 392 :si-vis-utilization 2788 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 5 0 1150 Wavelength setting as 800 is not available for TA