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The VLT-FLAMES Tarantula Survey. XV. VFTS 822: a candidate Herbig B[e] star at low metallicity

V. M. Kalari, J. S. Vink, P. L. Dufton, C. J. Evans, P. R. Dunstall, H. Sana, J. S. Clark, L. Ellerbroek, A. de Koter, D. J. Lennon, W. D. Taylor

TL;DR

The paper investigates whether VFTS 822, a B8-type emission-line star with a dusty disc in the LMC's 30 Doradus, is a young, accreting pre-main-sequence (PMS) object or an evolved B[e] supergiant in a low-metallicity environment. Using VLT-FLAMES spectroscopy and infrared/UV photometry, the authors derive T_eff ≈ 12,000 K, log g ≈ 2.6, and log L ≈ 4.04 L_sun, identify strong Balmer and metal emission, and detect a significant infrared excess indicating a dusty disc. They compute an accretion rate dot M_acc on the order of 3×10^-4 M_sun yr^-1 under PMS assumptions, yielding M_* ≈ 10 M_sun and an age near 3×10^4 yr, which supports a rare PMS B[e] interpretation at low metallicity, though an sgB[e] scenario remains possible. The study highlights the potential of measuring mass accretion rates at low metallicity and contributes to understanding how metallicity affects early stellar growth and B[e] phenomena in the LMC.

Abstract

We report the discovery of the B[e] star VFTS 822 in the 30 Doradus star-forming region of the Large Magellanic Cloud, classified by optical spectroscopy from the VLT-FLAMES Tarantula Survey and complementary infrared photometry. VFTS 822 is a relatively low-luminosity (log $L$ = 4.04 $\pm$ 0.25 $L_{\odot}$) B8[e] star. In this Letter, we evaluate the evolutionary status of VFTS 822 and discuss its candidacy as a Herbig B[e] star. If the object is indeed in the pre-main sequence phase, it would present an exciting opportunity to measure mass accretion rates at low metallicity spectroscopically, to understand the effect of metallicity on accretion rates.

The VLT-FLAMES Tarantula Survey. XV. VFTS 822: a candidate Herbig B[e] star at low metallicity

TL;DR

The paper investigates whether VFTS 822, a B8-type emission-line star with a dusty disc in the LMC's 30 Doradus, is a young, accreting pre-main-sequence (PMS) object or an evolved B[e] supergiant in a low-metallicity environment. Using VLT-FLAMES spectroscopy and infrared/UV photometry, the authors derive T_eff ≈ 12,000 K, log g ≈ 2.6, and log L ≈ 4.04 L_sun, identify strong Balmer and metal emission, and detect a significant infrared excess indicating a dusty disc. They compute an accretion rate dot M_acc on the order of 3×10^-4 M_sun yr^-1 under PMS assumptions, yielding M_* ≈ 10 M_sun and an age near 3×10^4 yr, which supports a rare PMS B[e] interpretation at low metallicity, though an sgB[e] scenario remains possible. The study highlights the potential of measuring mass accretion rates at low metallicity and contributes to understanding how metallicity affects early stellar growth and B[e] phenomena in the LMC.

Abstract

We report the discovery of the B[e] star VFTS 822 in the 30 Doradus star-forming region of the Large Magellanic Cloud, classified by optical spectroscopy from the VLT-FLAMES Tarantula Survey and complementary infrared photometry. VFTS 822 is a relatively low-luminosity (log = 4.04 0.25 ) B8[e] star. In this Letter, we evaluate the evolutionary status of VFTS 822 and discuss its candidacy as a Herbig B[e] star. If the object is indeed in the pre-main sequence phase, it would present an exciting opportunity to measure mass accretion rates at low metallicity spectroscopically, to understand the effect of metallicity on accretion rates.

Paper Structure

This paper contains 10 sections, 2 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Results
  3. VFTS spectroscopy
  4. Photometry
  5. Infrared properties
  6. Evolutionary status
  7. B[e] supergiant?
  8. Or Herbig B[e] star?
  9. $\dot{M}_{\text{acc}}$
  10. Conclusions

Figures (4)

  • Figure 1: Median FLAMES-Giraffe spectra of VFTS 822.
  • Figure 2: Observed fluxes in optical (circles) and IR (asterisks). The dashed line is the model SED and the solid line the best-fit YSO model.
  • Figure 3: H-R diagram showing the position of VFTS 822 (circle), LMC sgB[e] (squares), Galactic PMS B[e] (asterisks), model birthlines (dotted lines), MS (solid line), and PMS (dashed-dotted line) isochrones.
  • Figure 4: Spitzer 8 $\mu$m image showing the position of VFTS 822 (square) with respect to R136 (cross). North is up and east is to the left. Circles and diamonds are known Class I and Class II sources, respectively.