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: 7328
----- Attempting Submission 1 (Thu Apr 16 08:35:15 GMT 2026) -----The correct lifetime position of the G160M instrument has been checked and justified when necessary.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.
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.Please find attached the first submission of the Phase II of my proposal for full review. I am submitting with the warning that all FP-POS should be use for better data quality, but I am only using 3.-29562687----- Attempting Submission 1 (Mon Aug 10 16:41:10 GMT 2026) -----I am submitting with the warning that all FP-POS should be use for better data quality, but I am only using 3, which should be enough for my science case.Cygnus X-1, unraveling a well-known mystery: HST/COS spectroscopy of the stellar wind in the X-ray binary Cygnus X- 1.Black holes (BHs) paired with massive stars are among the most extreme objects in the universe. These systems - known as high-mass X-ray binaries - are unique cosmic laboratories and our closest windows into accretion physics around compact objects. Yet the stellar winds driving their accretion remain poorly understood. In the iconic high-mass X-ray binary system Cygnus X-1, the massive star continuously loses mass through its wind, which is captured by the BH, forming a bright accretion disk radiating in X-rays. This system regularly switches between two main accretion states in X-rays: a hard state - where the Comptonized emission from the hot inner plasma dominates - and a soft state - where the disk blackbody emission from the disk dominates. Crucially, X-rays directly alter the wind itself: a low X-ray flux in the hard state produces a faster, stronger wind, making multiwavelength observations essential. Yet despite decades of study, the Far-UV spectrum of Cygnus X-1 in the hard state has never been captured by the Hubble Space Telescope; a 2004 attempt failed due to instrument failure. This is the gap we will close. With HST/COS UV spectroscopy, simultaneously triggered with daily MAXI X-ray monitoring and high-resolution optical observations from our dedicated 2m telescope, we will deliver the first complete characterization of the stellar wind feeding a BH. Combined with state-of-the-art atmospheric models, these observations will resolve a long-standing mystery: how do massive stars feed BHs, and what drives the wind that sustains this cosmic powerhouse?Cygnus X-1 is a galactic black hole high-mass X-ray binary located at 2.2 kpc, has an orbital period of ~5.6 days and a V-magnitude of 8.91. This is a variable X-ray source, where changes in its emission track changes in the accretion disk. In this proposal, we aim to study the stellar wind of Cygnus X-1 in the hard X-ray spectral state, when the X-ray emission is the lowest, and the UV emission from the stellar wind is the strongest.
In order to get Cygnus X-1 in the hard state, we have one Disruptive ToO with a turn-around time lower than 3 weeks with 5 activations, with a 90% chance that the system remains in the hard state for more than 48 hours.
We were allocated 15 HST orbits and we need 15 spectra at different orbital phases of the system to apply the Fourier Disentangling method. Thus, we need 5 spectra per grating using the three following COS instruments: G130M/1096, G130M/1318, and G160M/1577. The corresponding science exposure times are ~3.0 ks, ~1.8 ks, and ~1.2 ks, respectively. The source is visible for ~53 mins over the 96 mins of one HST orbit. Hence, allowing on average only one grating to observe per HST orbit.
Since Cygnus X-1 advances by only ~0.01 in orbital phase between two consecutive HST orbits, we plan to observe with the three gratings over up to three consecutive HST orbits. This strategy ensures that the three spectra obtained during a given visit probe nearly identical orbital phases. We then wait approximately one day, corresponding to an orbital-phase shift of about 0.1, before repeating the sequence. Repeating this sequence over five visits will provide the required 15 spectra while achieving sufficiently broad and well-sampled orbital-phase coverage for the Fourier Disentangling analysis.Maimouna Brigitte has expertise in X-rays and optical observations, as well as in multi-wavelength spectral analysis. She studies the X-ray/optical anti-correlation in X-ray binary systems, and more precisely the High-Mass X-ray binary Cygnus X-1.
Dr. Jiri Svoboda is an expert in accretion physics. He studies black holes across their mass scale, from X-ray binaries to Active Galactic Nuclei. He has valuable experience in X-ray spectral analysis using various X-ray telescopes.
Dr. Varsha Ramachandran's research focuses on massive stars in low-metallicity galaxies. She studies the observational properties of massive stars and binaries in the Local Group. She has experienced in UV observations using the HST.
Dr. Brankica Kubatova's principal expertise is in the area of hot, massive stars and their winds. She is experienced in solving radiative transfer in inhomogeneous (i.e. clumped) stellar winds and in testing physical processes in stellar winds that influence the determination of mass-loss rates. She is also experienced in quantitative spectroscopy, i.e. the analysis of spectroscopic data using detailed quantitative modelling to obtain accurate values of stellar and wind parameters.
Dr. Petr Hadrava developed the Fourier Disentangling method to separate the spectral parameters of each component in a multiple system. He is an expert in optical observations, stellar winds, massive stars and spectroscopy.
Dr. Noel Castro Segura is an expert in multiwavelength spectroscopy of accreting compact binaries, with extensive experience in time-resolved ultraviolet observations with the Hubble Space Telescope. His expertise also includes the analysis of accretion-driven variability, stellar wind diagnostics, and coordinated multi-instrument campaigns spanning X-ray to optical wavelengths.Stellar Physics and Stellar TypesSupermassive Black Holes and Active Galaxies6falsefalsefalsefalsefalsefalsefalseSUPPORTEDSTARX-RAY TRANSIENTNOThis 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.J2000J2000COS/FUVSpectroscopicNoNoG130M1096COS/FUVSpectroscopicNoNoG130M1318COS/FUVSpectroscopicNoNoG160M1577/Users/brigitte/Downloads/HST_approved_proposal_PhaseII/OP-cache/18369_latest-v01.xmlThe scheduling data was generated by CASM 34.2.CASM was run in Phase II mode.(Tic-Visit
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