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Hydrogen line variability in B supergiant HD75149 arises from mass-loss rate episodes in a slow wind on day-long timescales.

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2026-06-29 09:31 UTC pith:FAGNG6M2

load-bearing objection This paper delivers a 21-year time series for HD75149 with a modeled factor-1.8 mass-loss jump in four days, but does not test whether pulsation-driven density changes could produce the same Halpha shifts. the 2 major comments →

arxiv 2605.29044 v1 pith:FAGNG6M2 submitted 2026-05-27 astro-ph.SR

Multi epoch spectroscopic variability of the B supergiant HD75149

J. Chamoun-Contreras , C. Arcos , N. Machuca , C. E. Perez-Ramirez , L. S. Cidale , M. Cur\'e , I. Araya , D. Turis-Gallo
show 1 more author
M. Hadjara
This is my paper
classification astro-ph.SR
keywords B supergiantHD75149spectroscopic variabilitystellar windsmass-loss rateHalpha P-Cygni profilesdelta-slow wind
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper analyzes 25 optical spectra of HD75149 spanning 2004 to 2025 to study its spectroscopic variability in a consistent hydrodynamical framework. Halpha shows pronounced changes in P-Cygni and emission profiles over intervals of a few days, while metal lines exhibit only small radial velocity amplitudes consistent with pulsations. Modeling with the ISOSCELES grid in the delta-slow regime indicates the mass-loss rate increased by a factor of 1.8 within four days, with terminal velocity remaining nearly constant. The contrast between hydrogen and other lines points to episodic mass loss as the driver, with no detected close binary companion.

Core claim

The pronounced variation observed in hydrogen lines, in contrast with the variability of other lines, suggests that it is due to mass-loss rate episodes driven by a slow wind occurring on a timescale comparable to photometric variations. The largest variation in the mass-loss rate corresponds to an increase of a factor of 1.8 within four days, while the terminal velocity remains barely affected.

What carries the argument

The ISOSCELES grid combined with the delta-slow hydrodynamic regime, used to model Halpha emission, absorption, and P-Cygni profiles and extract variable mass-loss rates and terminal velocities.

Load-bearing premise

The ISOSCELES grid and delta-slow regime accurately capture the conditions producing the observed Halpha changes without major contributions from pulsation-induced density variations or undetected companions.

What would settle it

Finding comparable variability amplitudes in metal lines inconsistent with pulsations, or detecting a close companion through extended radial velocity monitoring, or observing Halpha profile changes without corresponding mass-loss rate shifts in the models.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Mass-loss rate episodes in B supergiants can occur on timescales of a few days.
  • Terminal velocity of the wind stays stable during these mass-loss rate changes.
  • Hydrogen line variability can be directly linked to photometric variations through wind dynamics.
  • No evidence of a close binary companion appears in the radial velocity data.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Episodic mass loss could add to the total integrated mass lost by B supergiants beyond steady-state wind predictions.
  • Similar short-term wind variability may occur in other B supergiants that show comparable photometric fluctuations.
  • Longer-term monitoring could test whether the mass-loss episodes repeat at regular intervals or occur randomly.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The paper reports multi-epoch optical spectroscopy of B supergiant HD75149 (25 nightly-averaged spectra, 2004–2025), measuring RVs and EWs for 17 lines (H, He I, Si III, etc.). Hα shows pronounced variability including P-Cygni profile changes on timescales of days, while metal lines exhibit only small RV amplitudes. Using the ISOSCELES grid in the delta-slow hydrodynamic regime, the authors attribute the Hα changes to mass-loss rate episodes, with the largest reported variation being a factor of 1.8 increase in Ṁ within four days while v∞ remains nearly constant. They conclude that the hydrogen-line variability arises from slow-wind mass-loss episodes on timescales comparable to photometric variations and find no evidence for a close binary companion.

Significance. If the central attribution holds after quantitative exclusion of alternatives, the work would provide direct observational evidence linking short-term Hα profile evolution in a BSG to Ṁ variations within an existing hydrodynamic grid, with the reported factor-1.8 change on a four-day timescale offering a concrete, falsifiable datum for wind-variability models. The consistent multi-epoch line measurements and use of an existing grid constitute reproducible elements that strengthen the result if the modeling assumptions are validated.

major comments (2)
  1. [Modeling of Hα profiles] Modeling of Hα profiles (described after the line measurements): the attribution of P-Cygni and emission changes to Ṁ episodes (factor 1.8 in four days) rests on the ISOSCELES grid plus delta-slow regime being both necessary and sufficient, yet the manuscript provides no forward models with fixed Ṁ and pulsation-modulated density/velocity perturbations, nor χ² comparisons demonstrating that such fixed-Ṁ models fail to reproduce the observed Hα evolution while the variable-Ṁ grid succeeds. This omission directly affects the load-bearing claim that mass-loss episodes, rather than pulsation-driven density variations, drive the hydrogen-line changes.
  2. [Results on radial velocities and equivalent widths] Results on radial velocities and equivalent widths (17 lines): although metal-line RV amplitudes are reported as small and consistent with pulsations, the text does not quantify the expected Hα profile response under a fixed-Ṁ hydrodynamic solution with density perturbations at the observed pulsation periods, leaving open whether the observed Hα variability could be reproduced without invoking Ṁ changes.
minor comments (2)
  1. The abstract states that 25 spectra were analyzed but does not reference a table listing observation dates, instruments, or S/N values; adding such a table would improve traceability of the multi-epoch data.
  2. Notation for mass-loss rate (Ṁ) and terminal velocity (v∞) should be defined at first use in the modeling description for clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The two major comments both concern the strength of the evidence distinguishing mass-loss rate variations from pulsation-driven effects in the Hα modeling. We address each point below and will revise the manuscript to improve clarity and add supporting discussion.

read point-by-point responses

  1. Referee: Modeling of Hα profiles (described after the line measurements): the attribution of P-Cygni and emission changes to Ṁ episodes (factor 1.8 in four days) rests on the ISOSCELES grid plus delta-slow regime being both necessary and sufficient, yet the manuscript provides no forward models with fixed Ṁ and pulsation-modulated density/velocity perturbations, nor χ² comparisons demonstrating that such fixed-Ṁ models fail to reproduce the observed Hα evolution while the variable-Ṁ grid succeeds. This omission directly affects the load-bearing claim that mass-loss episodes, rather than pulsation-driven density variations, drive the hydrogen-line changes.

    Authors: We agree that the manuscript does not contain explicit forward models with fixed Ṁ plus pulsation-modulated perturbations or χ² model comparisons. The attribution rests on the ISOSCELES grid fits in the delta-slow regime providing acceptable matches only when Ṁ is allowed to vary, combined with the small observed metal-line RV amplitudes. In revision we will expand the modeling section to include a quantitative estimate of the Hα profile response expected from density perturbations at the observed pulsation periods (scaled from the measured RV amplitudes) under fixed Ṁ, and we will state the limitations of the current grid-based approach more explicitly. revision: yes

  2. Referee: Results on radial velocities and equivalent widths (17 lines): although metal-line RV amplitudes are reported as small and consistent with pulsations, the text does not quantify the expected Hα profile response under a fixed-Ṁ hydrodynamic solution with density perturbations at the observed pulsation periods, leaving open whether the observed Hα variability could be reproduced without invoking Ṁ changes.

    Authors: The manuscript reports the small metal-line RV amplitudes but does not provide the requested quantification of the corresponding Hα variability under fixed Ṁ. We will revise the results and discussion sections to add this estimate, using the observed RV periods and amplitudes to scale the expected density perturbations and assess whether they can account for the observed Hα changes without Ṁ variation. This addition will directly address the open question raised. revision: yes

Circularity Check

0 steps flagged

No significant circularity: observational measurements and external grid application remain independent of fitted outputs.

full rationale

The paper reports direct RV/EW measurements from 25 spectra and applies the pre-existing ISOSCELES grid plus delta-slow regime to fit observed Hα profiles, yielding a reported factor-1.8 Ṁ variation. No step defines a quantity in terms of itself, renames a fit as a prediction, or reduces the central attribution to a self-citation chain or ansatz smuggled from the authors' prior work. The modeling framework is treated as an external tool whose validity is assumed rather than derived within the paper; the variability claim rests on the contrast between H-line and metal-line behavior in the data, not on any tautological reduction. This is the normal case of an observational study using established tools.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on the applicability of the ISOSCELES grid and delta-slow regime to interpret Halpha variability as mass-loss episodes; these are domain assumptions rather than new derivations.

free parameters (1)
  • mass-loss rate scaling
    Fitted to match observed Halpha emission and P-Cygni profiles; the factor 1.8 change is derived from this fit.
axioms (1)
  • domain assumption delta-slow hydrodynamic regime governs the wind structure
    Invoked when modeling Halpha profiles with the ISOSCELES grid.

pith-pipeline@v0.9.1-grok · 5897 in / 1309 out tokens · 24939 ms · 2026-06-29T09:31:06.464672+00:00 · methodology

0 comments
read the original abstract

Massive stars continuously enrich the surrounding interstellar medium by supplying it with stellar material driven by their powerful winds. B supergiant stars (BSGs) in particular are a type of massive star characterized by strong winds and notable photometric and spectroscopic variability. We aim to conduct a pilot study of the optical spectroscopic variability of the BSG HD75149 between 2004 and 2025. Its extended temporal baseline and pronounced variability amplitude make it particularly well suited for investigating the physical origin of the observed short-term variability within a consistent hydrodynamical and radiative-transfer framework. We analyzed 25 nightly averaged optical spectra obtained with different instruments and telescopes, some of them with observations over several consecutive days. We measured the radial velocities (RVs) and equivalent widths (EWs) of 17 spectral lines (H, HeI, SiIII, NII, MgII, CII). We modeled the Halpha emission, absorption, and P-Cygni profiles using the ISOSCELES grid and the delta-slow hydrodynamic regime. Halpha shows variability in intervals of a few days, including P-Cygni changes, while metal lines show small RV amplitudes, consistent with pulsating oscillations. The largest variation in the mass-loss rate corresponds to an increase of a factor of 1.8 within four days. In contrast, the terminal velocity remains barely affected during the same time interval. The pronounced variation observed in hydrogen lines, in contrast with the variability of other lines, suggests that it is due to mass-loss rate episodes driven by a slow wind occurring on a timescale comparable to photometric variations. We found no evidence of a close binary companion in the sample used, but we cannot completely exclude the possibility of a wide or low-inclination companion.

Figures

Figures reproduced from arXiv: 2605.29044 by C. Arcos, C. E. Perez-Ramirez, D. Turis-Gallo, I. Araya, J. Chamoun-Contreras, L. S. Cidale, M. Cur\'e, M. Hadjara, N. Machuca.

Figure 1
Figure 1. Figure 1: Left: Hα emission, absorption, and P-Cygni profiles over the years 2004–2025. The star exhibits short-term variability on a daily basis. Right: Si iii 4552 Å absorption line for the same period but without the spectrum of 2025. The spectral lines are shifted 27.89 km s−1 from the central position. No significant intensity variation is observed for this atomic line. For both images, a color code is assigned… view at source ↗
Figure 3
Figure 3. Figure 3: Absolute RVs for He i 4471 (oranges circles) and Si iii 4552 (blue squares) spectral lines. The data presented cover observations made in 2014 (March–April) and 2015 (February–March). Both lines show a similar temporal behavior, especially during the second period . N ii 4607 shows slight variations; however, in 2015 there was a period of greater variation with a peak of ∼10.5 km s−1 , although most of the… view at source ↗
Figure 2
Figure 2. Figure 2: From top to bottom: EW (M0), RV (M1), and skewness ⟨v 3 ⟩ (M3) for Cii 6578.05 line. The measurements are concentrated in two main observing groups around 2014 and 2015. The EW values remain within a relatively narrow range compared to the RV and skewness, whereas the RV and ⟨v 3 ⟩ panels exhibit greater scatter and several high-value points in the central and later observing groups. 3.3. Silicon lines The… view at source ↗
Figure 4
Figure 4. Figure 4: Hα line profile variation of each time interval between 2013 and 2025. The solid black lines represent the fitted spectra, with the corre￾sponding fits overplotted in red. Solid gray lines represent spectra within the time interval that were not used in the modeling. (Si iii, N ii, Mg ii, Cii) and the absence of coherent periodicity across epochs argue against the presence of a short-period bi￾nary compani… view at source ↗

discussion (0)

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