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Orbital and Physical Properties of the Pleiades Binary 27 Tau (Atlas)

T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash

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Pith's one-line read The paper shows that Atlas, a 291-day binary in the Pleiades, has its primary star measurably flattened by rotation, and uses that shape plus spectroscopy and astrometry to establish a 1% distance, precise masses, and a possible…

desk verdict A careful, well-documented orbital analysis that delivers a solid 1% distance and good masses for Atlas, with the oblateness and spin-orbit claims being genuinely interesting but model-limited and in need of a gravity-darkened follow-up. read the letter →

arxiv 2507.15933 v1 pith:UIKZOA2Z submitted 2025-07-21 astro-ph.SR astro-ph.GA

G. Torres (CfA) , A. Tkachenko , K. Pavlovski , S. Gossage , G. H. Schaefer , C. Melis , M. Ireland , J. D. Monnier
show 7 more authors
N. Anugu S. Kraus C. Lanthermann K. Gordon R. Klement S. J. Murphy R. M. Roettenbacher
This is my paper · ORCID
classification astro-ph.SRastro-ph.GA
keywords PleiadesAtlas(27Tau)orbitalparallaxbinarymassesstellaroblatenessrapidrotationhelium-weakstarlong-baselineinterferometry
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

Atlas, the second-brightest star in the Pleiades, has been known for decades as a 291-day binary, but its distance and stellar properties remained imprecise enough to leave room for disagreement. This paper combines new high-resolution spectra, long-baseline interferometry, lunar-occultation chords, and the Hipparcos intermediate astrometric data in one joint fit, aiming to pin down the three-dimensional orbit, the distance, and the masses of both components. The fit returns a distance of $136.2 \pm 1.4$ pc, masses of $5.04 \pm 0.17$ and $3.64 \pm 0.12$ $M_\odot$, and an apparent stellar disk for the rapidly rotating primary that is measurably elliptical, with an axis ratio of $0.8456 \pm 0.0076$. From that shape the authors infer a true oblateness $R_{\mathrm{pol}}/R_{\mathrm{eq}} = 0.828 \pm 0.057$, a spin axis that may be aligned with the orbit, and an initial rotation of about 55% of breakup in rotating stellar-evolution models. If these claims hold, Atlas becomes the most distant star with a directly measured rotational flattening and a benchmark for the upper main sequence of the Pleiades.

What carries the argument

The load-bearing mechanism is a joint Markov-chain Monte Carlo orbital fit that ingests radial velocities, resolved astrometry from several interferometers, lunar-occultation chords, and one-dimensional Hipparcos abscissa residuals, while also fitting the squared visibilities and closure phases directly. For the primary's disk geometry the paper replaces a circular limb-darkened disk with a limb-darkened ellipse whose diameter along a baseline at position angle PA is $\varphi_1(\mathrm{PA}) = \varphi_{\min}/\sqrt{1-e_\phi^2\cos^2(\mathrm{PA}-\theta_\phi)}$ (Eq. 1), yielding the apparent flattening. To convert apparent to true shape it solves two equations jointly: the projection relation $\varphi_{\min} = \sqrt{\varphi_{\mathrm{pol}}^2 \sin^2 i + \varphi_{\mathrm{maj}}^2 \cos^2 i}$ (Eq. 2) and the uniform-rotation, point-mass relation $v_{\mathrm{eq}} = \sqrt{(2GM/R_{\mathrm{pol}})(1 - R_{\mathrm{pol}}/R_{\mathrm{eq}})}$ (Eq. 3), with the measured $v \sin i$ providing the third constraint. The same machinery feeds rotating evolutionary tracks, adjusted for gravity darkening, to compare predicted temperature, radius, equatorial velocity, and oblateness with the measured values.

What would settle it

Future interferometric imaging that resolves the primary's surface brightness beyond a single ellipse would settle it: if the apparent shape is accompanied by significant gravity darkening or a latitude-dependent rotation profile, the uniform-rotation toy model cannot fit the data and the quoted oblateness and spin orientation change. A simpler check is a direct measurement of the spin inclination, for example from asteroseismic pulsations or from orbital geometry, and if it disagrees with $i = 64^\circ \pm 20^\circ$, the chain linking $v \sin i$, the ellipse, and the oblateness breaks.

Watch

Extended reading notes

Core claim

The central claim is that the full orbital solution for Atlas is geometric: a 290.9919-day eccentric orbit with angular semimajor axis $12.9896 \pm 0.0036$ mas, an orbital parallax of $7.340 \pm 0.076$ mas, and masses $M_1 = 5.04 \pm 0.17\,M_\odot$, $M_2 = 3.64 \pm 0.12\,M_\odot$. The second, independent claim is that the primary's apparent disk is an ellipse, not a circle, with minor axis $0.4523 \pm 0.0026$ mas and apparent axis ratio $0.8456 \pm 0.0076$, which the authors interpret as rotational flattening. Combining the ellipse with the measured $v \sin i = 217$ km/s and a hydrostatic point-mass model gives a true oblateness $R_{\mathrm{pol}}/R_{\mathrm{eq}} = 0.828 \pm 0.057$, an equatorial velocity of $233 \pm 45$ km/s, and a spin inclination of $64^\circ \pm 20^\circ$; the spin axis may coincide with the orbital axis, with a mutual angle $\psi = 21^\circ \pm 12^\circ$. The paper also establishes that the secondary is a helium-weak chemically peculiar star with strong Fe, Cr, and Ti anomalies, and that rotating evolutionary models started at about 55% of critical rotation reproduce the primary's global properties at an age of 102\textendash106 Myr, near the end of its main-sequence life.

Load-bearing premise

The whole physical interpretation of the flattened disk rests on the assumption that the primary is a uniformly rotating, hydrostatic star with a point-mass gravitational potential and no gravity darkening; if differential rotation or gravity darkening is substantial, the inferred inclination, polar radius, oblateness, and spin-orbit angle all shift, and the evolutionary-model conclusions inherit that shift.

Editorial extensions

If this is right

  • The Pleiades distance from Atlas becomes $136.2 \pm 1.4$ pc, about 1% and in line with the cluster mean of 135.3 pc, effectively closing the old tension between Hipparcos and ground-based distances for this star.
  • An oblate shape measured at 136 pc would extend the small sample of directly resolved rapidly rotating stars, previously confined to within about 50 pc, to a Pleiades member, demonstrating that the technique works at cluster distances.
  • If the spin and orbital axes are aligned within $21^\circ \pm 12^\circ$, the system formed or evolved with nearly coplanar angular momenta, and future tidal-evolution calculations for a 5+3.6 $M_\odot$ pair at 1.77 au should reproduce this.
  • The oblateness and $v_{\mathrm{eq}}$ measurement break the degeneracy between convective overshoot and initial rotation in the models, identifying $\omega_0/\omega_{\mathrm{crit}} \approx 0.55$ and an age of 102\textendash106 Myr, comparable to other Pleiades age estimates.
  • The secondary's helium-weak, Fe/Cr/Ti-rich spectrum, together with its magnetic field and variable line profiles, makes Atlas a binary in which a chemically peculiar star orbits a normal, rapidly rotating primary.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A fuller gravity-darkened model with a Roche surface would likely revise the oblateness and spin-axis angle by more than the quoted formal errors; the difference between that model and the present toy model is a direct, testable measure of the neglected physics.
  • If the spin-orbit alignment survives better data, it suggests that whatever process left the secondary chemically peculiar and magnetic did not randomize the system's angular momentum, constraining the magnetic companion's formation history.
  • Applying the same multi-epoch joint fit to the other Pleiades binaries with dynamical masses would yield a cluster distance independent of moving-cluster assumptions, and could reveal whether the Hipparcos bias the authors quantify here is universal or source-specific.
  • The 2.428 d photometric period, which the authors note cannot be rotation of the primary, could be tested as rotation of the secondary at an inclination of $44^\circ \pm 10^\circ$; time-resolved spectra at that period would check whether the line-profile variations repeat on that timescale.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 4 minor

Summary. This paper presents a joint MCMC orbital analysis of the Pleiades binary 27 Tau (Atlas) that combines new CfA/TRES radial velocities, new and archival CHARA interferometry (PAVO, CLIMB, MIRC-X, MYSTIC) analyzed directly at the visibility level, published Mark III/PTI/NPOI astrometry, lunar occultation measurements, and Hipparcos abscissa residuals. With 34 adjustable parameters and per-dataset error-inflation factors, the authors derive a 290.99-day orbit with semimajor axis 1.768 ± 0.018 au, an orbital parallax of 7.340 ± 0.076 mas (distance 136.2 ± 1.4 pc), and masses M1 = 5.04 ± 0.17 M☉ and M2 = 3.64 ± 0.12 M☉. The primary's disk is modeled as a limb-darkened ellipse (Eq. 1) with apparent axial ratio 0.8456 ± 0.0076; Section 8.1 converts this into a true oblateness Rpol/Req = 0.828 ± 0.057, an inclination of 64° ± 20° (or 116° ± 20°), and a spin-orbit angle ψ = 21° ± 12°, under assumptions the paper labels a 'toy model.' A MESA comparison selects an initial rotation rate ω0/ωcrit ≈ 0.55 and an age of 102–106 Myr. The secondary is identified as a helium-weak chemically peculiar star with variable line profiles.

Significance. The dynamical results are a genuine advance: Atlas joins the small set of Pleiades binaries with dynamical masses, and the 1% orbital parallax provides an independent anchor for the cluster distance that is consistent with kinematic moving-cluster estimates and with the known Hipparcos bias, which the authors quantify by simulation. Methodological strengths include the use of Hipparcos abscissa residuals rather than catalog orbital parameters, error-inflation factors estimated per dataset, corrections of published sign errors in the Pan et al. astrometry and of the lunar occultation tabulation, machine-readable radial-velocity tables, and the stated intention to release the calibrated visibilities in OIFITS format. If the primary's flattening survives a gravity-darkened re-analysis, Atlas would be the most distant star with a directly measured rotational flattening and one of the few binaries with a quantitative spin-orbit comparison; the MESA model also makes falsifiable predictions (ω/ωcrit ≈ 0.77 at the current age; polar–equatorial temperature difference ≈ 650 K). The secondary's atmospheric analysis (He-weak, Fe/Cr/Ti enhanced) is a useful, clearly separated result.

major comments (3)
  1. [7.2, Eq. (1)] The limb-darkened elliptical disk model of Eq. (1) neglects gravity darkening, and the fitted parameters ϕmin, eϕ, and θϕ will absorb the wavelength- and position-angle-dependent brightness redistribution of a rapid rotator into a biased geometric ellipse; the ~20σ significance of the apparent axial ratio is a statement within this model family only. The authors explicitly acknowledge the limitation in §7.2 ('the formal errors reported above may not reflect the true uncertainties'), yet the abstract and §8.1 report Rpol/Req = 0.828 ± 0.057 and ψ = 21° ± 12° as results, with the uncertainties merely doubled by an uncalibrated factor. The spectroscopic v sin i = 217 ± 9 km s−1 that enters Eq. (3) is likewise a disk-averaged quantity that gravity darkening and differential rotation would shift. The orbital elements, parallax, and masses in Table 6 do not depend on this model and appear well supported; the concern is confined to the flattening, spin-orbit, and MESA initial-rotation claims. I request either a gravity-darkened re-fit of the existing CHARA visibilities (an analytic gravity-darkened ellipsoid with an Espinosa Lara–Rieutord or von Zeipel law would be a natural first step) or a forward-model bias calculation using the MESA-predicted temperature contrast (ΔT ≈ 650 K, ω/ωcrit ≈ 0.77) to quantify the resulting bias on ϕmin, eϕ, and θϕ.
  2. [8.1, Eqs. (2)–(3)] The conversion in §8.1 assumes uniform rotation, hydrostatic equilibrium, and a point-mass potential, so the inferred veq = 233 ± 45 km s−1, Rpol, and oblateness inherit those assumptions, as the paper notes. The reported spin-orbit angle, however, is conditional on a discrete branch choice: the inclination has a two-fold ambiguity (64° or 116°) and θϕ carries an unresolvable 180° ambiguity in Eq. (1). Up to the ψ ↔ 180°−ψ degeneracy, the four combinations give ψ ≈ 17° and ψ ≈ 46° under the point estimates, and the paper quotes ψ = 21° ± 12° from the favorable branch only. The qualitative conclusion ('may well be aligned') is robust to this choice given the large uncertainties, but I recommend reporting ψ for the alternative branch (or a branch-averaged value) so that the numerical result does not depend on a selection made after the fit. Note also that the difference between the major-axis orientation (θϕ = −9.9°) and the line of nodes (Ω = 334.2°) is 15.9°, several times the doubled formal uncertainty of θϕ, so the alignment conclusion remains contingent on unquantified systematics.
  3. [8.3, Fig. 10] Section 8.3 and Fig. 10 apply Espinosa Lara & Rieutord (2011) gravity-darkening corrections to the MESA model predictions, but the measured oblateness and veq used in the same comparison are taken from the §7.2 toy-model ellipse that omits gravity darkening; the comparison is thus asymmetric, with the effect included on one side and absent on the other. Furthermore, the initial rate ω0/ωcrit ≈ 0.55 is selected by matching Teff and log g at the nominal mass, and the argument that the measured shape and equatorial velocity lift the fov–ω0 degeneracy is then validated against the same model-dependent oblateness and veq. The quoted consistency in the lower panels of Fig. 10 is therefore not an independent confirmation; the age range (102–106 Myr) is less affected because it is set mainly by mass and Teff. I recommend recomputing this comparison with a gravity-darkened model of the primary disk, or explicitly re-derating the ω0/ωcrit constraint and the 'good consistency' claims as conditional on the toy model.
minor comments (4)
  1. [Table 6] The error-inflation priors are described in §7.1 as log-uniform, but the bracketed ranges shown for f_RV1, f_RV2, f_P, f_Z, f_occ, and f_Hip are [−5, 5], over which a log-uniform density is undefined; if the uniform prior applies to log10 f, the table should say so explicitly.
  2. [Table 3] The note suggesting that the flagged 1991 occultation point is a misprint (ρocc = 3.1 mas instead of 13.1 mas) is post-hoc speculation about a measurement the authors chose to exclude; either include the corrected value in the fit or remove the speculation from the discussion of the reported solution.
  3. [Abstract] The abstract's statement that the spin axis 'may well be aligned with the orbital axis' does not carry the caveats that the alignment is conditional on the toy-model disk, on the favorable branch choice for i and θϕ, and on unquantified gravity-darkening systematics; I suggest adding an explicit hedge.
  4. [§3.1, footnote 20] The adopted wavelength correction factors for MIRC-X and MYSTIC (1.0054 ± 0.0006 and 1.0067 ± 0.0007) and the limb-darkening coefficients for the three bandpasses are given in prose; collecting these calibration values in a table would make the analysis easier to reproduce.

Circularity Check

1 steps flagged · score 5.0 of 10

MESA initial-rotation inference is partly circular: the current rotation rate and oblateness are outputs of a track whose initial rotation was tuned to those same observables, then cited as a theoretical prediction. Orbit, masses, and distance remain non-circular.

  1. fitted input called prediction [Section 8.3 (MESA comparison; paragraphs following 'In Figure 10...' and 'Convective core overshooting...')]
    "Extensive tests indicated ... a model for a star spinning at an initial rate of about 55% ... reaches a satisfactory agreement with the spectroscopically measured Teff and our two estimates of log g ... the point at which the model most closely matches the temperature ... corresponds to a rapid rotation rate of ω/ωcrit ≈ 0.77. Consequently, theory predicts ... a significantly distorted stellar structure ... as we actually observe. ... our estimates of the current shape and equatorial rotation of the primary ... constrain the initial rotation to be near the value we report."

    The initial rotation rate ω0/ωcrit ≈ 0.55 is not derived from first principles; it is the value that the authors say matches the primary's measured Teff, log g, current shape, and equatorial rotation. The model with this input then yields a current rotation ω/ωcrit ≈ 0.77 and a distorted structure. Presenting the latter as 'theory predicts ... as we actually observe' is circular because the observed distortion and equatorial rotation were among the constraints used to select ω0; the agreement is a consistency check of the calibrated model, not an independent prediction. The orbit, masses, and distance do not share this circularity.

full rationale

The paper's core orbit, masses, orbital parallax, and distance (Table 6) come from a joint MCMC fit to RVs, CHARA visibilities/closure phases, Pan/Zwahlen interferometry, Hipparcos abscissae, and lunar occultations; these are external data and no circularity is present. The spectroscopic Teff, log g, v sin i, and abundances are also independent model-atmosphere fits. The main circularity is confined to the MESA comparison: ω0/ωcrit ≈ 0.55 was selected to reproduce the measured Teff, log g, current shape, and equatorial rotation, and then the same model's current ω/ωcrit ≈ 0.77 and distorted structure are presented as a theoretical prediction ('as we actually observe'). That is a calibrated consistency check rather than a prediction; it does not invalidate the measured oblateness, which stands on the interferometric ellipse fit, but it does mean the evolutionary 'prediction' of distortion is partly an output of the fit. The spin-orbit alignment estimate is highly model-dependent and ambiguous (two inclination solutions), but this is a caveat about robustness, not circularity. No load-bearing self-citation chain was found.

Assumptions & free parameters 10 free parameters · 7 assumptions · 0 invented entities

No new physical entities are introduced; the wide companion claimed in the WDS catalog is argued to be spurious. The ledger is dominated by modeling assumptions and fitted parameters in the rotation and evolution comparison. The orbital elements themselves are direct fits to data and are listed only for completeness; the parameters that most affect the interpretive claims are the MESA initial rotation rate, overshooting, mixing length, and the ellipse/limb-darkening model for the primary.

free parameters (10)
  • Initial rotation rate omega0/omega_crit (MESA) = 0.55
    Chosen by extensive tests to match the measured Teff, log g, radius, oblateness, and veq of the primary; central to the derived initial rotation and age.
  • Convective core overshooting parameter fov = 0.016
    Adopted from MIST models and Claret and Torres (2019); affects model radius, age, and blue-hook position.
  • Mixing length parameter alpha_ML = 1.82
    Adopted from MIST calculations; affects convective envelope structure.
  • Primary apparent ellipse parameters (phi_min, e_phi, theta_phi) = 0.4523 mas, 0.534, -9.9 degrees
    Fitted to CHARA visibilities and closure phases; basis for the oblateness claim.
  • Secondary angular diameter phi_2 = 0.20 mas
    Fixed based on estimated radius and distance; the secondary is unresolved in the data.
  • Limb-darkening coefficients for PAVO, H, and K bands = 0.312, 0.164, 0.138 (primary); 0.295, 0.149, 0.126 (secondary)
    Adopted from Claret and Bloemen (2011); enter the visibility model for the primary disk.
  • Error scale factors f_RV1, f_RV2, f_P, f_Z, f_occ, f_Hip and jitter terms = 0.518, 1.67, 0.679, 0.86, 1.90, 0.83, plus sigma_V2 and sigma_CP values
    Fitted to bring reduced chi-square near unity; affect quoted uncertainties rather than physical claims.
  • Orbital and systemic fit parameters = See Table 6; e.g., P=290.9919 d, a=12.9896 mas, K1=27.09 km/s, K2=37.63 km/s
    Fitted simultaneously in the MCMC but tightly constrained by RVs, interferometry, occultations, and Hipparcos residuals; they are measured model parameters rather than ad hoc constants.
  • Spectroscopic radius ratio R1/R2 = 2.33 ± 0.07
    Free parameter in the gssp binary analysis; used with the primary radius to infer the secondary radius.
  • Hipparcos astrometric corrections and photocenter semimajor axis = delta_alpha*=+0.03 mas, delta_delta=-0.85 mas, delta_mu_alpha*=+0.44 mas/yr, delta_mu_delta=+0.07 mas/yr…
    Fitted to Hipparcos abscissa residuals so the data constrain the orbit while allowing a Pleiades parallax offset.
assumptions (7)
  • domain assumption Spectral disentangling assumes line profiles are constant in shape over time apart from orbital Doppler shifts.
    Used in Section 4; violated by the secondary's phase-dependent line-profile distortions described in Sections 5 and 6, so the atmospheric parameters of both stars carry unquantified systematics.
  • domain assumption The primary's projected disk is a limb-darkened ellipse with no gravity darkening, and the star is in hydrostatic equilibrium with uniform rotation and a point-mass gravitational potential.
    Eq. 1 in Section 7.2 and Eqs. 2 and 3 in Section 8.1; the paper calls this a toy model and doubles the formal uncertainties.
  • domain assumption Model atmospheres for the secondary with fixed He, Fe, Cr, and Ti abundances capture its atmospheric structure.
    Section 5; ignores possible vertical stratification and other abundance anomalies, acknowledged in Section 8.3 as a source of potential bias.
  • domain assumption Hipparcos abscissa residuals can be modeled with catalog position and parallax offsets that are not forced to equal the orbital parallax.
    Section 7.1; avoids the known Pleiades parallax bias but introduces five additional free corrections.
  • domain assumption The MESA rotation implementation based on Roche potential fits, with diffusive overshooting fov=0.016, is adequate for a 5 solar mass B star near critical rotation.
    Section 8.3; PARSEC with similar parameters is about 500 K hotter, so the model choice matters for the age and rotation conclusions.
  • domain assumption The secondary's angular diameter can be fixed at 0.20 mas based on estimated radius and distance.
    Section 7.1; the secondary is unresolved, so this fixed value enters the visibility model.
  • domain assumption Lunar occultation measurements without reported uncertainties can be assigned an error of 0.4 mas.
    Table 3 note; a minor but nonzero contributor to the orbital constraints.

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Pith. "Pith review of Orbital and Physical Properties of the Pleiades Binary 27 Tau (Atlas)." pith.science (2026). https://pith.science/paper/UIKZOA2Z

@misc{pith2026250715933,
  author       = {Pith},
  title        = {Pith review of: Orbital and Physical Properties of the Pleiades Binary 27 Tau (Atlas)},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/UIKZOA2Z}},
  note         = {Machine review of arXiv:2507.15933}
}
abstract

We report new spectroscopic and interferometric observations of the Pleiades binary star Atlas, which played an important role nearly three decades ago in settling the debate over the distance to the cluster from ground-based and space-based determinations. We use the new measurements, together with other published and archival astrometric observations, to improve the determination of the 291-day orbit and the distance to Atlas ($136.2 \pm 1.4$ pc). We also derive the main properties of the components, including their absolute masses ($5.04 \pm 0.17 M_{\odot}$ and $3.64 \pm 0.12 M_{\odot}$), sizes, effective temperatures, projected rotational velocities, and chemical composition. We find that the more evolved primary star is rotationally distorted, and are able to estimate its oblateness and the approximate orientation of its spin axis from the interferometric observations. The spin axis may well be aligned with the orbital axis. Models of stellar evolution from MESA that account for rotation provide a good match to all of the primary's global properties, and point to an initial angular rotation rate on the zero-age main sequence of about 55% of the breakup velocity. The current location of the star in the H-R diagram is near the very end of the hydrogen-burning main sequence, at an age of about 105 Myr, according to these models. Our spectroscopic analysis of the more slowly-rotating secondary indicates that it is a helium-weak star, with other chemical anomalies.

Figures

Figures reproduced from arXiv: 2507.15933 by the authors.

Figure 1
Figure 1. Top: Two of our observed spectra of Atlas (black) at opposite quadratures (maximum velocity separation). Bottom: Disentangled spectra of the binary components in the spectral re￾gion 4430–4530 ˚A, centered on the He I 4471 ˚A and Mg II 4481 ˚A lines. The secondary component is shifted upward by 0.04, for clar￾ity. of SPD (Simon & Sturm 1994; Hadrava 1995), the or￾bital elements of the binary system and the component… view at source ↗
Figure 2
Figure 2. Comparison between the disentangled spectra (solid black line) and best-fit model (dashed red line) for the primary and secondary components of the Atlas system. Two different wavelength regions are shown, featuring Hγ and a section rich in metal lines. Note the changing vertical scales in the four panels [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 4
Figure 4. An observed composite LSD profile (black solid line) fitted with a superposition of two model LSD profiles (red solid line). The black and blue dashed lines show the respective model LSD profiles of the primary and secondary components. Residu￾als, obtained by subtracting the composite model profile from the observations, are shown with a black dotted line at the top, shifted upward by 0.01, for clarity [PITH_FULL_… view at source ↗
Figures from the paper (7 more)
Figure 5
Figure 5. Figure 5: LSD profiles of the secondary component, shifted to zero velocity, obtained after subtracting the primary’s contribu￾tion from the composite average profiles. The red dots are the measurements, and the solid blue lines represent spline fits to the profiles. The spectra…
Figure 6
Figure 6. Figure 6: Limb-darkened diameter of the primary of Atlas as a function of the baseline orientation (PA). The points represent in￾dependent diameter estimates over separate PA intervals, with the horizontal error bars indicating the range in each set. The measure￾ment in parenthe…
Figure 7
Figure 7. Figure 7: RV measurements for Atlas with our model. The center-of-mass velocity is indicated with the dotted line. Resid￾uals are shown at the bottom [PITH_FULL_IMAGE:figures/full_fig_p010_7.png]
Figure 8
Figure 8. Figure 8: Interferometric observations of Atlas from Pan et al. (2004) (shown in red) and Zwahlen et al. (2004) (blue). Error ellipses represent the uncertainty on each axis, and short line seg￾ments connect the measurement with the predicted position on the orbit. The one-dimen…
Figure 9
Figure 9. Figure 9: Kinematic determinations of the distance to Atlas (moving cluster method), based on its proper motion from various sources, as labeled on the x axis. Also indicated are the few direct determinations from the trigonometric parallax, as well as our or￾bital parallax resu…
Figure 10
Figure 10. Figure 10: Comparison of the measured properties of the primary of Atlas against theory. The blue line corresponds to our MESA model for the nominal mass of M1 = 5.04 M⊙ determined in this work, Solar metallicity was assumed. The initial rotation rate was set to ω0/ωcrit = 0.55,…
Figure 11
Figure 11. Figure 11: Similar to [PITH_FULL_IMAGE:figures/full_fig_p016_11.png]

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