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REVIEW 4 major objections 5 minor 75 references

A combined optical and infrared survey of 53 B and A stars around the Orion Nebula identifies 30 pre-main-sequence candidates, several previously catalogued as evolved giants.

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2026-08-01 23:27 UTC pith:JGLQLFSD

load-bearing objection Useful spectral catalog with a real external mass check; the PMS ages/candidates rest on a distance prior that can bias the near-5 Myr objects, so take the candidate counts as provisional. the 4 major comments →

arxiv 2607.15409 v1 pith:JGLQLFSD submitted 2026-07-16 astro-ph.SR

Pre-main Sequence B Stars Surrounding the Orion Nebula

P.H.F.B. Braz , A. Roman-Lopes , W.J.B. Corradi , E. B. Am\^ores , M. S. Angelo , F. S. S. Maia , J. F. C. Santos Jr. , A. E. Piatti
show 1 more author
W. Reis
This is my paper
classification astro-ph.SR
keywords pre-main sequenceB starsOrion Nebulaspectral classificationisochrone fittingHerbig Ae/Be starseclipsing binariesstar formation
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.

This paper tries to establish that the immediate surroundings of the Orion Nebula contain a substantial population of very young B-type stars still contracting toward the main sequence, and that several of these were previously misidentified as evolved supergiants or giants. If correct, it would mean that the 'evolved' B stars in this benchmark star-forming region are actually short-lived pre-main-sequence objects, providing rare empirical anchors for the formation of intermediate-mass stars. The authors derive spectral types, masses, and ages for 53 stars, reclassifying many as class V instead of class I–III, and use a distance- and reddening-corrected isochrone fit across three photometric surveys to place 30 stars on the PMS track.

Core claim

The central claim is that dozens of B and early A stars surrounding the Orion Nebula — including several previously assigned luminosity classes I through III — are not evolved stars but pre-main-sequence objects. By combining infrared Brackett-line and optical helium, silicon, and magnesium line ratios for spectral classification and fitting PARSEC isochrones to Gaia, 2MASS, and WISE photometry, the authors identify 30 PMS candidates (13 robust, 13 likely, 4 peculiar) and show that the isochrone-derived masses agree with dynamical masses from eclipsing binaries. This agreement is presented as validation of both the spectral types and the age–mass estimates, and the age distribution of the PM

What carries the argument

The load-bearing tools are (1) a refined empirical relation between the equivalent widths of the near-infrared Brackett lines Br11 and Br13 and spectral type, calibrated on template stars, and (2) a chi-square minimization of PARSEC isochrones in three colour–magnitude diagrams (Gaia, 2MASS, WISE) that yields age and mass per star. The independent check is a Gaussian fit to dynamical masses of eclipsing binaries per spectral subtype, which sets the expected mass range for each B subtype and thereby anchors the isochrone solutions.

Load-bearing premise

The strongest load-bearing premise is that the age-split distance moduli (≈385 pc for stars older than 5 Myr, ≈410 pc for younger) and the uniform reddening of E(B−V)=0.1 are correct for each individual star; because these values are fed into the isochrone fit that then determines age and PMS status, a systematic error in distance or reddening would shift stars between the PMS and MS groups.

What would settle it

Measure surface gravities (log g) from high-resolution spectra for the 30 PMS candidates. True PMS stars of a given spectral type should show lower surface gravity than MS stars of the same type; if the candidates all show MS-like log g values, the PMS classification collapses. Alternatively, re-fit the isochrones using individual Gaia parallaxes instead of the adopted age-split distance moduli; if most candidates then fall on the main-sequence tracks, the central claim fails.

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

If this is right

  • The Orion Nebula region harbors at least 30 PMS B/A candidates, significantly more than previously recognized in this area.
  • Several stars with luminosity class I–III in older catalogues are reclassified as class V, changing the evolutionary picture of the early-type population around the ON.
  • The isochrone-derived masses agree with dynamical masses from eclipsing binaries, supporting the reliability of both the spectral classifications and the age–mass estimates.
  • The age distribution of PMS candidates suggests multiple or sequential star formation episodes around the ON, with younger early-type stars possibly triggered by feedback from older populations.
  • The combined optical+IR + photometric + dynamical-mass framework offers a transferable method for distinguishing PMS from evolved early-type stars in other star-forming regions.

Where Pith is reading between the lines

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

  • If these reclassifications hold, the 'evolved' B-star populations in other nearby star-forming regions may also be partially composed of PMS objects, implying that the census of young intermediate-mass stars is systematically underestimated.
  • The paper's reliance on a pre-imposed age–distance relation (older stars at ~385 pc, younger at ~410 pc) could be tested with individual Gaia parallaxes; such a test could either tighten or overturn the PMS classification for the borderline cases.
  • The spectroscopic variability seen in several candidates (HD 36827, HD 37025, HD 37334, HD 37428, V1133 Ori) makes them prime targets for time-domain spectroscopy, which could independently reveal binarity or disc accretion.
  • Because the sample deliberately excludes heavily reddened embedded stars, the true number of PMS B stars around the ON may be larger than 30; future infrared surveys with better nebula penetration could find more.

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

4 major / 5 minor

Summary. Braz et al. present a combined optical and near-infrared spectroscopic study of 53 B and early-A stars within 2 degrees of the Orion Nebula, for 48 of which they derive spectral classifications. They estimate stellar ages and masses by chi-square fitting of PARSEC isochrones to Gaia, 2MASS, and WISE colour-magnitude diagrams, using a spectroscopically informed mass prior and an independent calibration against eclipsing-binary dynamical masses. The paper identifies 30 PMS candidates, 13 of which are labelled robust, and reclassifies several stars previously assigned luminosity classes I–III as young class V objects. The authors argue that the resulting age distribution is consistent with sequential star formation in the Orion region.

Significance. If the identification of a sizable population of PMS B stars around the Orion Nebula is correct, this would be a valuable contribution to the census of young early-type stars and to constraints on the formation timescales of intermediate-mass stars. The paper has notable strengths: it combines optical and IR spectroscopy, makes use of an external dynamical-mass calibration, and provides a detailed target table. However, the central PMS claim rests on isochrone ages that are partly constructed from an age-dependent distance prior, and the dynamical-mass comparison does not validate the age step. The significance is therefore real but conditional on the analysis being repeated in a way that removes this circularity.

major comments (4)
  1. [Section 4, distance modulus paragraph] The isochrone fit uses (m−M)0=7.95 (~385 pc) for τ≥5 Myr and 8.1 (~410 pc) for τ<5 Myr; that is, the distance modulus is chosen from the model age before the fit. This creates a circular dependence between the distance prior and the fitted age. The quoted uncertainties vary the modulus by ±0.1, but not the age-dependent assignment itself. Many of the 13 'robust PMS' candidates in Section 5 have best-fit ages between 2 and 6 Myr in Table 2 (e.g. #3, #4, #5, #11, #16, #29, #36, #41–44, #47, #49), so their classification sits precisely where the 0.15 mag modulus jump matters. Please repeat the analysis using individual Gaia parallax distances, or marginalise over distance, and demonstrate that the PMS/MS classification is stable when the age-distance coupling is removed.
  2. [Section 4, uniform reddening; Table 3] A uniform E(B−V)=0.1 is adopted for all stars, yet the template-matching reddenings in Table 3 range from 0.02 to 0.26 mag, and the reddening maps quoted in the text give averages between 0.083 and 0.178 depending on resolution. Only six outliers are re-fitted with revised reddenings in Section 6.3. For the remaining stars, including most PMS candidates, an error of 0.1–0.2 mag in E(B−V) shifts a star’s CMD position by an amount comparable to the separation between isochrones in Figure 5. Please either re-derive ages and masses using individual reddening estimates for all stars with available spectra, or provide a quantitative demonstration that the PMS/MS classification is invariant under the full plausible range of E(B−V).
  3. [Section 4, final paragraph] The agreement with the eclipsing-binary masses of Eker et al. (2018) checks that the isochrone masses are consistent with a spectral-type–mass relation, but it carries no information about stellar age. The sentence stating that this agreement 'supports the reliability of both our spectral classifications and age determinations' overinterprets the validation: the dynamical masses validate the mass scale and spectral types, not the ages or the PMS classification. Please revise the claim and provide an age-sensitive external test, or explicitly acknowledge that the ages are not independently validated.
  4. [Section 5, first paragraph] The 'robust PMS' group is defined as stars 'consistently found on the PMS track in all three CMDs'. This is not an independent confirmation because the three CMDs are fit with the same PARSEC isochrones, the same extinction law, the same uniform reddening, and the same age-dependent distance rule. The consistency is partly built into the fitting procedure. Please show, for at least one CMD, the positions of these stars with a distance that does not depend on the fitted age (e.g., individual parallaxes), or compare with an independent isochrone set, before claiming robustness.
minor comments (5)
  1. [Throughout] There are several typographical errors, including 'noticible' (Section 3) and 'circunstellar' (Section 4). Please proofread carefully.
  2. [Section 2.1 / Section 5.1] Table 1 lists seven runaway candidates (#3, #4, #33, #39, #42, #43, #47), but Section 5.1 says that 'almost all of the runaways candidates are located in relatively gas-free regions ... such as the stars #6, 28, 40, and 52'. The latter are not in Table 1. Please clarify which stars are being referred to.
  3. [Table 2, star #43] The WISE-based uncertainties for #43 are reported as age 2.0+0.0−0.0 Myr and mass 2.9±0.0 M☉. A zero mass uncertainty is surprising; please state whether this is a grid-quantisation artefact and how often it occurs.
  4. [Section 3, Eq. (1)] The Brackett-line calibration is based on template stars selected from Ramírez-Preciado et al. (2020), but the template list and the residual scatter of the fit are not given. Please include the template stars and the rms scatter of Eq. (1) so the ±1 subtype uncertainty can be evaluated.
  5. [Section 2, initial selection] The initial CMD selection uses isochrones corrected for a single distance modulus of 8.00 mag, while the subsequent fit uses 7.95/8.1 depending on age. It would be useful to state whether any targets were retained or rejected solely because of this 0.05–0.1 mag difference in the selection step.

Circularity Check

1 steps flagged

Age-dependent distance modulus in Section 4 couples the fitted age to the input distance, partially forcing the PMS classification.

specific steps
  1. self definitional [Section 4, first paragraph (distance-modulus correction) and the isochrone chi-square fit; Table 2; Section 5 PMS candidates]
    "For the distance modulus correction, we adopted two different values depending on stellar age: older populations (τ≥5Myr) are located closer to us, with (m−M)0=7.95 (~385pc), while younger populations (τ<5Myr) have (m−M)0=8.1 (~410pc) ... The adopted age and mass correspond to the point in the isochrone that minimises the χ2 value."

    The age τ is the quantity being solved by χ² minimisation against isochrones, but the isochrones are shifted by a distance modulus that depends on whether τ<5 or τ≥5 Myr. Thus the test is not a blind photometric comparison at a fixed distance: the τ<5 Myr models are displaced by 0.15 mag relative to the τ≥5 Myr models, which is comparable to the ±0.1 distance-modulus uncertainty quoted later in the section. A star near the 5 Myr boundary can therefore be pushed onto either side of the PMS/MS divide by this prior rather than by its photometry. The robust PMS list contains many stars with best-fit ages of 2–6 Myr (e.g. indices 3, 4, 5, 11, 16, 29, 36, 41–44, 47, 49), exactly in the switch region. The age–distance split is itself justified only by cited prior work, including Maia et al. (2010

full rationale

The central circular content is the age-dependent distance modulus in Section 4. The paper adopts (m−M)0=7.95 for τ≥5 Myr and 8.1 for τ<5 Myr, then fits τ by χ² minimisation of isochrones shifted by that same age-dependent distance. This couples the fitted output to the model input and can force borderline stars into either the PMS or MS category. The robust PMS candidates include several stars with ages around 2–6 Myr, where the 0.15 mag switch is decisive, so the PMS classification is partly constructed rather than purely measured. However, the paper has substantial independent content: the reclassification of formerly class I–III stars is supported by spectroscopic class-V features and template matching, and the isochrone masses are checked against eclipsing-binary dynamical masses. Thus the circularity is real but partial, not a complete reduction of the central claim to its inputs. Score 4 reflects this partial circularity with independent grounding.

Axiom & Free-Parameter Ledger

4 free parameters · 5 axioms · 0 invented entities

The central claim rests on externally supplied inputs: PARSEC isochrones, an extinction law, eclipsing-binary mass calibration, and an age-split distance modulus. The age-split distance modulus is a genuine circular input; the uniform reddening and single-metallicity assumptions are simplifications. No new physical entities are introduced.

free parameters (4)
  • Uniform reddening E(B−V) = 0.1 mag
    Adopted for all 53 stars in the isochrone fitting (Sect. 4), although individual estimates range from 0.02 to 0.26 mag; directly shifts CMD positions and derived ages/masses.
  • Age-dependent distance modulus = (m−M)0 = 8.1 for τ<5 Myr; 7.95 for τ≥5 Myr
    Chosen from the age being derived (Sect. 4); makes the age fit partly self-fulfilling and is the main circular input.
  • IR Brackett-line spectral-type calibration = Slope 0.798, intercept 6.961 (Eq. 1)
    Least-squares relation fit to template stars from Ramírez-Preciado et al. (2020), which shares an author with this paper; used to classify B2–A0 stars.
  • Average metallicity [M/H] = −0.2
    APOGEE ASPCAP average over 1032 stars adopted for all isochrones (Sect. 4); an input that affects ages/masses.
axioms (5)
  • domain assumption PARSEC isochrones v3.8 accurately model pre-main-sequence and main-sequence evolution of B/A stars at 0.1–11 Myr.
    Invoked in Sect. 4 to convert photometry into ages/masses; no independent check of early-type PMS tracks is given.
  • domain assumption Cardelli et al. (1989) extinction law with R_V=3.1 holds across the ON sample.
    Sect. 4; individual stars with R_V=3.36 and 3.83 are treated as exceptions, so the uniform law is load-bearing.
  • ad hoc to paper The age-dependent foreground distance relation (older Orion populations at ~385 pc, younger at ~410 pc) applies to each star individually.
    Sect. 4 uses this to set (m−M)0 before fitting ages; it is the main circular input.
  • domain assumption Template stars and line-ratio diagnostics are unaffected by binarity, nebular contamination, or chemical peculiarity.
    Sect. 3 and 6; several stars show nebular lines, narrow lines, magnetic peculiarities, or companions, so this is not guaranteed.
  • domain assumption Eclipsing-binary mass ranges (Eker et al. 2018) are representative of the ON B-star population and can validate isochrone masses.
    Sect. 4/Table 4; external benchmark, but field binary masses may differ from the young ON population.

pith-pipeline@v1.3.0-alltime-deepseek · 3725 in / 3575 out tokens · 191134 ms · 2026-08-01T23:27:53.857762+00:00 · methodology

0 comments
read the original abstract

Pre-main sequence (PMS) early-type stars are rare due to their rapid evolution. Confirming PMS B stars is accordingly valuable for constraining higher mass star formation scenarios. Although the Orion Nebula (ON) region offers an ideal laboratory for such studies, its population of B stars remains poorly characterized. We aim to determine spectral types, masses, and ages of B and early A stars surrounding the ON, to identify robust PMS candidates. We combine optical and near-infrared spectroscopy to estimate spectral types using Brackett, He, Si, and Mg lines. Photometry from Gaia, 2MASS, and WISE is used to construct colour-magnitude diagrams to fit isochrones via chi-square minimisation, yielding stellar ages and masses. Dynamical masses from eclipsing binaries are employed as independent constraints on the mass range allowed for each spectral subtype. We derive stellar ages and masses for 53 stars and spectral classifications for 48 of them, identifying 30 PMS candidates, including some that were previously assigned to luminosity classes I-III. Several stars show spectroscopic variability, potentially linked to circumstellar material or binarity. Our combined spectroscopic and photometric approach identifies robust PMS B-star candidates and provides a validated framework for distinguishing them from evolved counterparts - in this instance, refining the census of early-types young stars in Orion. The age distribution of the PMS candidates offers preliminary clues about the star formation history of the ON region.

Figures

Figures reproduced from arXiv: 2607.15409 by A. E. Piatti, A. Roman-Lopes, E. B. Am\^ores, F. S. S. Maia, J. F. C. Santos Jr., M. S. Angelo, P.H.F.B. Braz, W.J.B. Corradi, W. Reis.

Figure 1
Figure 1. Figure 1: CMDs (top panels) and skymap (bottom panel) of the sample selection from the Gaia, 2MASS, and WISE crossmatch, considering sources with 2 ≤ 𝜛 ≤ 3 mas located within 2◦ of the ON. The top panels show the Gaia, 2MASS and WISE CMDs, respectively. In each CMD, the early-type candidates selected in this work are outlined in black, while the dashed lines indicate the 1, 5, and 10 Myr isochrones for visual guidan… view at source ↗
Figure 2
Figure 2. Figure 2: Histogram of 𝜇𝛼 (blue) and 𝜇𝛿 (red) for the selected sample of early-type candidates surrounding the ON region. The dashed lines represent the adopted kinematics boundaries at ±3 mas/yr for the ON population [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Spectra of HD 37700 (#48) (black solid line) and B6V (red) and B8V (blue) spectra template, in the IR and optical range in the top and bottom panel, respectively. The optical spectra of HD 37700 and the template stars are from the LAMOST DR10 survey. The lines used for spectral classification, together with the Balmer series lines, are marked in both panels. 1.0 1.5 2.0 2.5 3.0 F / F 5 5 0 0 Å HD 37700 Pic… view at source ↗
Figure 4
Figure 4. Figure 4: Best fit of the observed optical spectra of HD 37700 (#48) (blue solid line) corrected by 𝐸 (𝐵−𝑉) = 0.07 mag and the Pickles (1998) template spectra (black dashed line) in the top panel. In the bottom panel, the relative residual difference (red solid line) is shown, with the zero dashed line shown for visual guidance [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: CMDs of Gaia (left panel), 2MASS (middle panel), and WISE (right panel) surveys with propagated photometric errors for each star. The squares represent stars with only IR spectra, while the triangles represent objects with both optical and IR spectra. Isochrones of different ages are plotted with distinct colours and symbols, as indicated in the legend, spanning from 0.3 Myr (darker colours) to 5.0 Myr (li… view at source ↗
Figure 6
Figure 6. Figure 6: Mass estimate for each star in our sample (blue circles) and for the eclipsing binary stars from Eker et al. (2018) with their corresponding uncertainties (black circles with error bars), derived from Gaussian fit. Stars later than A0 were grouped with the A0 subtype, as the mass difference among these spectral types is not significant [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Age-spectral type diagram of B and early-A type candidates sur￾rounding the Orion Nebula region. Stellar ages were derived from a Monte Carlo simulation, with the median age adopted as the representative age and the 16th and 84th percentiles as the lower and upper uncertainties, respec￾tively. The blue squares, green triangles, and red circles represent the robust, likely, and peculiar PMS candidate groups… view at source ↗

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Works this paper leans on

75 extracted references · 7 canonical work pages

  1. [1]

    , keywords =

    The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data. , keywords =. doi:10.3847/1538-4365/ac4414 , archivePrefix =. 2112.02026 , primaryClass =

    arXiv

  2. [2]

    , keywords =

    Spectral Classification of Stars in A Supplement to the Bright Star Catalogue. , keywords =. doi:10.1086/423803 , adsurl =

    work page doi:10.1086/423803

  3. [3]

    , keywords =

    Circumstellar disks around Herbig Be stars. , keywords =. doi:10.1051/0004-6361/200810401 , archivePrefix =. 0812.1636 , primaryClass =

    Pith/arXiv arXiv

  4. [4]

    Orion revisited. I. The massive cluster in front of the Orion nebula cluster. , keywords =. doi:10.1051/0004-6361/201220119 , archivePrefix =. 1209.3787 , primaryClass =

    Pith/arXiv arXiv

  5. [5]

    , keywords =

    Evolution over time of the Milky Way's disc shape. , keywords =. doi:10.1051/0004-6361/201628461 , archivePrefix =. 1701.00475 , primaryClass =

    Pith/arXiv arXiv

  6. [6]

    , keywords =

    The FORS1 catalogue of stellar magnetic field measurements. , keywords =. doi:10.1051/0004-6361/201526497 , archivePrefix =. 1508.03839 , primaryClass =

    Pith/arXiv arXiv

  7. [7]

    Handbook of Star Forming Regions, Volume I , year = 2008, editor =

    Overview of the Orion Complex. Handbook of Star Forming Regions, Volume I , year = 2008, editor =. doi:10.48550/arXiv.0812.0046 , adsurl =

    Pith/arXiv arXiv doi:10.48550/arxiv.0812.0046 2008

  8. [8]

    Orion revisited. II. The foreground population to Orion A. , keywords =. doi:10.1051/0004-6361/201323191 , archivePrefix =. 1402.1034 , primaryClass =

    Pith/arXiv arXiv

  9. [9]

    Braz , P. H. F. B. Espectroscopia das estrelas jovens HD\,141569, HD\,144432, HD\,163296 e o aglomerado aberto NGC\,1981

    1981

  10. [10]

    , keywords =

    PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code. , keywords =. doi:10.1111/j.1365-2966.2012.21948.x , archivePrefix =. 1208.4498 , primaryClass =

    arXiv 2012

  11. [11]

    , keywords =

    Herbig Stars. , keywords =. doi:10.1007/s11214-023-00949-z , archivePrefix =. 2301.01165 , primaryClass =

    Pith/arXiv arXiv

  12. [12]

    Stars and brown dwarfs in the Orionis cluster. IV. IDS/INT and OSIRIS/GTC spectroscopy and Gaia DR2 astrometry. , keywords =. doi:10.1051/0004-6361/201935987 , archivePrefix =. 1908.10340 , primaryClass =

    Pith/arXiv arXiv 1908

  13. [13]

    , keywords =

    Pre-main-sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns. , keywords =. doi:10.3847/1538-4357/aca324 , archivePrefix =. 2211.06454 , primaryClass =

    Pith/arXiv arXiv

  14. [14]

    , keywords =

    The Relationship between Infrared, Optical, and Ultraviolet Extinction. , keywords =. doi:10.1086/167900 , adsurl =

    doi:10.1086/167900

  15. [15]

    New Be Stars, Line Identifications, and Line Profiles

    High-Resolution H-Band Spectroscopy of Be Stars With SDSS-III/Apogee: I. New Be Stars, Line Identifications, and Line Profiles. , keywords =. doi:10.1088/0004-6256/149/1/7 , archivePrefix =. 1409.4668 , primaryClass =

    Pith/arXiv arXiv

  16. [16]

    , keywords =

    Spectroscopic variability of massive pre-main-sequence stars in M17. , keywords =. doi:10.1051/0004-6361/202347369 , archivePrefix =. 2310.04287 , primaryClass =

    Pith/arXiv arXiv

  17. [17]

    , keywords =

    Updated parameters of 1743 open clusters based on Gaia DR2. , keywords =. doi:10.1093/mnras/stab770 , archivePrefix =. 2103.12829 , primaryClass =

    Pith/arXiv arXiv

  18. [18]

    , keywords =

    A parsec-scale Galactic 3D dust map out to 1.25 kpc from the Sun. , keywords =. doi:10.1051/0004-6361/202347628 , archivePrefix =. 2308.01295 , primaryClass =

    Pith/arXiv arXiv

  19. [19]

    , keywords =

    Interrelated main-sequence mass-luminosity, mass-radius, and mass-effective temperature relations. , keywords =. doi:10.1093/mnras/sty1834 , archivePrefix =. 1807.02568 , primaryClass =

    Pith/arXiv arXiv

  20. [20]

    , keywords =

    The Herbig Ae/Be stars associated with nebulosity. , keywords =

  21. [21]

    Summary of the content and survey properties

    Gaia Data Release 3. Summary of the content and survey properties. , keywords =. doi:10.1051/0004-6361/202243940 , archivePrefix =. 2208.00211 , primaryClass =

    Pith/arXiv arXiv

  22. [22]

    Astrophysical Bulletin , keywords =

    On Properties of Main Sequence Magnetic Stars. Astrophysical Bulletin , keywords =. doi:10.1134/S1990341319010073 , adsurl =

    work page doi:10.1134/s1990341319010073

  23. [23]

    Stellar Spectral Classification

  24. [24]

    VISION - Vienna survey in Orion. III. Young stellar objects in Orion A. , keywords =. doi:10.1051/0004-6361/201832577 , archivePrefix =. 1810.00878 , primaryClass =

    Pith/arXiv arXiv

  25. [25]

    Discovery of coherent radial gas motions at the 100-pc scale

    3D dynamics of the Orion cloud complex. Discovery of coherent radial gas motions at the 100-pc scale. , keywords =. doi:10.1051/0004-6361/202038913 , archivePrefix =. 2007.07254 , primaryClass =

    Pith/arXiv arXiv 2007

  26. [26]

    , keywords =

    Stellar parameters and evidence of circumstellar activity for a sample of Herbig Ae/Be stars. , keywords =. doi:10.1051/0004-6361:20065005 , adsurl =

    work page doi:10.1051/0004-6361:20065005

  27. [27]

    , year = 1960, month = mar, volume =

    The Spectra of Be- and Ae-Type Stars Associated with Nebulosity. , year = 1960, month = mar, volume =. doi:10.1086/190050 , adsurl =

    doi:10.1086/190050 1960

  28. [28]

    , keywords =

    Herbig Ae/Be Stars in nearby OB Associations. , keywords =. doi:10.1086/426918 , archivePrefix =. astro-ph/0410494 , primaryClass =

    Pith/arXiv arXiv

  29. [29]

    Michigan catalogue of two-dimensional spectral types for the HD Stars ; vol. 5

  30. [30]

    , keywords =

    Evidence for Environmental Dependence of the Upper Stellar Initial Mass Function in Orion A. , keywords =. doi:10.1088/0004-637X/764/2/114 , archivePrefix =. 1212.1171 , primaryClass =

    Pith/arXiv arXiv

  31. [31]

    , keywords =

    Chemically peculiar stars on the pre-main sequence. , keywords =. doi:10.1051/0004-6361/202348926 , archivePrefix =. 2405.08946 , primaryClass =

    arXiv

  32. [32]

    , keywords =

    Boron depletion in Galactic early B-type stars reveals two different main sequence star populations. , keywords =. doi:10.1051/0004-6361/202450896 , archivePrefix =. 2405.18266 , primaryClass =

    Pith/arXiv arXiv

  33. [33]

    Binarity from proper motion anomaly

    Stellar and substellar companions of nearby stars from Gaia DR2. Binarity from proper motion anomaly. , keywords =. doi:10.1051/0004-6361/201834371 , archivePrefix =. 1811.08902 , primaryClass =

    Pith/arXiv arXiv

  34. [34]

    The APOGEE-2 Survey of the Orion Star-forming Complex. II. Six-dimensional Structure. , keywords =. doi:10.3847/1538-3881/aad1f1 , archivePrefix =. 1805.04649 , primaryClass =

    Pith/arXiv arXiv

  35. [35]

    , keywords =

    The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function. , keywords =. doi:10.1016/j.physrep.2014.02.001 , archivePrefix =. 1402.0867 , primaryClass =

    Pith/arXiv arXiv 2014

  36. [36]

    , keywords =

    Kinematics in Young Star Clusters and Associations with Gaia DR2. , keywords =. doi:10.3847/1538-4357/aaef8c , archivePrefix =. 1807.02115 , primaryClass =

    Pith/arXiv arXiv

  37. [37]

    , keywords =

    A new automated tool for the spectral classification of OB stars. , keywords =. doi:10.1051/0004-6361/202040224 , archivePrefix =. 2110.10669 , primaryClass =

    Pith/arXiv arXiv

  38. [38]

    Research in Astronomy and Astrophysics , year = 2012, month = sep, volume =

    The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Research in Astronomy and Astrophysics , year = 2012, month = sep, volume =. doi:10.1088/1674-4527/12/9/003 , adsurl =

    doi:10.1088/1674-4527/12/9/003 2012

  39. [39]

    The astrometric solution

    Gaia Early Data Release 3. The astrometric solution. , keywords =. doi:10.1051/0004-6361/202039709 , archivePrefix =. 2012.03380 , primaryClass =

    Pith/arXiv arXiv 2012

  40. [40]

    , keywords =

    Characterization and photometric membership of the open cluster NGC1981. , keywords =. doi:10.1111/j.1365-2966.2010.17034.x , archivePrefix =. 1005.3047 , primaryClass =

    arXiv 2010

  41. [41]

    Validating the classification of variable young stellar object candidates

    Gaia Data Release 3. Validating the classification of variable young stellar object candidates. , keywords =. doi:10.1051/0004-6361/202244101 , archivePrefix =. 2206.05796 , primaryClass =

    Pith/arXiv arXiv

  42. [42]

    The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds. II. The Spatial Distribution and Demographics of Dusty Young Stellar Objects. , keywords =. doi:10.3847/0004-6256/151/1/5 , archivePrefix =. 1511.01202 , primaryClass =

    Pith/arXiv arXiv

  43. [43]

    An atlas of stellar spectra, with an outline of spectral classification

  44. [44]

    Vistas in Astronomy , year = 1966, month = jan, volume =

    Some characteristics of the orion association. Vistas in Astronomy , year = 1966, month = jan, volume =. doi:10.1016/0083-6656(66)90023-7 , adsurl =

    work page doi:10.1016/0083-6656(66)90023-7 1966

  45. [45]

    , keywords =

    High-Mass Star and Massive Cluster Formation in the Milky Way. , keywords =. doi:10.1146/annurev-astro-091916-055235 , archivePrefix =. 1706.00118 , primaryClass =

    Pith/arXiv arXiv

  46. [46]

    , keywords =

    The discovery of lambda Bootis stars - the Southern Survey II. , keywords =. doi:10.1093/mnras/staa2347 , archivePrefix =. 2008.02392 , primaryClass =

    Pith/arXiv arXiv 2008

  47. [47]

    Protostars and Planets IV , year = 2000, editor =

    Properties and Evolution of Disks around Pre-Main-Sequence Stars of Intermediate Mass. Protostars and Planets IV , year = 2000, editor =

    2000

  48. [48]

    New grid of northern standards for the spectral classification of B-type stars

    The IACOB project: XII. New grid of northern standards for the spectral classification of B-type stars. , keywords =. doi:10.1051/0004-6361/202449298 , archivePrefix =. 2407.04163 , primaryClass =

    arXiv

  49. [49]

    , keywords =

    First firm spectral classification of an early-B pre-main-sequence star: B275 in <ASTROBJ>M 17</ASTROBJ>. , keywords =. doi:10.1051/0004-6361/201118089 , archivePrefix =. 1110.5755 , primaryClass =

    Pith/arXiv arXiv

  50. [50]

    , keywords =

    A Stellar Spectral Flux Library: 1150-25000 A. , keywords =. doi:10.1086/316197 , adsurl =

    doi:10.1086/316197

  51. [51]

    Research Notes of the American Astronomical Society , keywords =

    GHOST Reduced Data Products for the Gemini Observatory Community and Beyond. Research Notes of the American Astronomical Society , keywords =. doi:10.3847/2515-5172/ad9f5f , archivePrefix =. 2412.13239 , primaryClass =

    Pith/arXiv arXiv

  52. [52]

    Universe , year = 2021, month = dec, volume =

    Searching for Magnetospheres around Herbig Ae/Be Stars. Universe , year = 2021, month = dec, volume =. doi:10.3390/universe7120489 , adsurl =

    work page doi:10.3390/universe7120489 2021

  53. [53]

    , keywords =

    A census of OB stars within 1 kpc and the star formation and core collapse supernova rates of the Milky Way. , keywords =. doi:10.1093/mnras/staf083 , archivePrefix =. 2503.08286 , primaryClass =

    Pith/arXiv arXiv

  54. [54]

    , keywords =

    Spectral Classification of B Stars: The Empirical Sequence Using SDSS-IV/APOGEE Near-IR Data. , keywords =. doi:10.3847/1538-4357/ab8127 , archivePrefix =. 2003.09469 , primaryClass =

    Pith/arXiv arXiv 2003

  55. [55]

    , keywords =

    Massive pre-main-sequence stars in M17. , keywords =. doi:10.1051/0004-6361/201629503 , archivePrefix =. 1704.08216 , primaryClass =

    Pith/arXiv arXiv

  56. [56]

    Photometric content and validation

    Gaia Early Data Release 3. Photometric content and validation. , keywords =. doi:10.1051/0004-6361/202039587 , archivePrefix =. 2012.01916 , primaryClass =

    Pith/arXiv arXiv 2012

  57. [57]

    Magnetic Fields of CP Stars in the Orion OB1 Association. IV. Stars of Subgroup 1b. Astrophysical Bulletin , keywords =. doi:10.1134/S1990341321010090 , archivePrefix =. 2104.02434 , primaryClass =

    Pith/arXiv arXiv

  58. [58]

    Research in Astronomy and Astrophysics , keywords =

    A Catalog and Statistical Analysis for Magnetic Stars. Research in Astronomy and Astrophysics , keywords =. doi:10.1088/1674-4527/ace9b0 , archivePrefix =. 2307.12315 , primaryClass =

    Pith/arXiv arXiv

  59. [59]

    , keywords =

    Kinematic study of the Orion Complex: analysing the young stellar clusters from big and small structures. , keywords =. doi:10.1093/mnras/stae2157 , archivePrefix =. 2409.09206 , primaryClass =

    Pith/arXiv arXiv

  60. [60]

    VizieR Online Data Catalog: Catalogue of stellar spectral classifications

  61. [61]

    , keywords =

    The Two Micron All Sky Survey (2MASS). , keywords =. doi:10.1086/498708 , adsurl =

    doi:10.1086/498708

  62. [62]

    , keywords =

    APOGEE Net: An Expanded Spectral Model of Both Low-mass and High-mass Stars. , keywords =. doi:10.3847/1538-3881/ac4de7 , archivePrefix =. 2201.03661 , primaryClass =

    Pith/arXiv arXiv

  63. [63]

    The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R -0.5ex 2500. , keywords =. doi:10.1088/0067-0049/193/2/24 , archivePrefix =. 1101.4002 , primaryClass =

    Pith/arXiv arXiv

  64. [64]

    , keywords =

    A new catalogue of members and candidate members of the Herbig Ae/Be (HAEBE) stellar group. , keywords =

  65. [65]

    , keywords =

    Three-dimensional extinction maps: Inverting inter-calibrated extinction catalogues. , keywords =. doi:10.1051/0004-6361/202243319 , archivePrefix =. 2205.09087 , primaryClass =

    Pith/arXiv arXiv

  66. [66]

    , keywords =

    Investigation of 131 Herbig Ae/Be Candidate Stars. , keywords =. doi:10.1086/379553 , adsurl =

    work page doi:10.1086/379553

  67. [67]

    , keywords =

    Identification and Spectroscopic Characterization of 128 New Herbig Stars. , keywords =. doi:10.3847/1538-4357/ac5c46 , archivePrefix =. 2202.01234 , primaryClass =

    Pith/arXiv arXiv

  68. [68]

    X-Ray Sources in Regions of Star Formation. I. The Naked T Tauri Stars. , keywords =. doi:10.1086/164367 , adsurl =

    work page doi:10.1086/164367

  69. [69]

    Baltic Astronomy , keywords =

    Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range. Baltic Astronomy , keywords =

  70. [70]

    , keywords =

    The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance. , keywords =. doi:10.1088/0004-6256/140/6/1868 , archivePrefix =. 1008.0031 , primaryClass =

    Pith/arXiv arXiv

  71. [71]

    , keywords =

    The Angular Momentum Evolution of 0.1-10 M _ solar Stars from the Birth Line to the Main Sequence. , keywords =. doi:10.1086/380503 , archivePrefix =. astro-ph/0310280 , primaryClass =

    Pith/arXiv arXiv

  72. [72]

    , keywords =

    The Gaia-ESO Survey: 3D dynamics of young groups and clusters from GES and Gaia EDR3. , keywords =. doi:10.1093/mnras/stae1806 , archivePrefix =. 2311.08358 , primaryClass =

    Pith/arXiv arXiv

  73. [73]

    , keywords =

    Structure, kinematics, and ages of the young stellar populations in the Orion region. , keywords =. doi:10.1051/0004-6361/201935781 , archivePrefix =. 1906.07002 , primaryClass =

    Pith/arXiv arXiv 1906

  74. [74]

    , keywords =

    Toward Understanding Massive Star Formation. , keywords =. doi:10.1146/annurev.astro.44.051905.092549 , archivePrefix =. 0707.1279 , primaryClass =

    Pith/arXiv arXiv

  75. [75]

    , keywords =

    Absolute magnitudes of B emission line stars : correlation between the luminosity excess and the effective temperature. , keywords =