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ATel #12237: A B1-2e optical classification for the optical counterpart of XTE J0052-723 (SXP 4.78; Swift J005139.2-721704)

Building upon our previous ATel #12224 we managed to obtain an optical spectrum of the counterpart. The full text follows:

ATel #12237; G. Maravelias (NOA), V. Antoniou (TTU/SAO), K. Boutsia (LCO), A. Zezas (UoC/SAO), A. Z. Bonanos (NOA), F. Haberl (MPE), D. Hatzidimitriou (UoA/NOA)

on 21 Nov 2018; 23:36 UT /

In ATel #12224 we reported the Hα emission, derived from a wide-field photometric survey of the Small Magellanic Cloud (Maravelias et al. 2017, IAUS 329, 373; Maravelias et al. 2019, in prep.), of the proposed optical counterpart source [M2002] 20671 to the X-ray transient XTE J0052-723 pulsar (SXP 4.78; Swift J005139.2-721704; ATel #12209). In addition to this clear detection, the work of Bonanos et al. (2010, AJ, 140, 416) showed that the IR colors of this source ([2dFS]0811; J=15.54 mag, J-[3.6]=0.56 mag) are indicative of a “photometric” Be star, defined as sources with an intrinsic color of JIRSF-[3.6]>0.5 mag.

However, to confirm the nature of the counterpart optical spectroscopy is needed. We obtained optical spectra using the LDSS-3 spectrograph on the 6.5m Clay/Magellan telescope (Las Campanas Observatory). The observations were performed on Nov. 20, 2018, acquiring two exposures of 600s each with a 1″ slit using the VPH-All grism (resulting in a 2630 — 10859 Å wavelength range, at a nominal dispersion of 1.9 Å/pix). The spectrum shows a clear single-peaked Hα line in emission, with a corresponding equivalent width of -10.65±0.14 Å. This is the first optical spectroscopic confirmation of the presence of Hα in emission. We note that Hβ appears in emission as well.

The spectral classification was based on the blue part of the spectrum and the classification scheme used in Maravelias et al. (2014, MNRAS, 438, 2005). The presence of the OII+CIII 4640-4650 blend and the strong HeI 4471 line point to an early-type star (spectral type up to B2), which is consistent with the absence of the MgII 4481 line and the weak SiII 4552 triplet line. The HeII 4200 and 4686 lines, which are indicative of B0.5 and earlier-spectral types, are absent, thus pointing to later types.

Combining these criteria we constrain the optical classification to a B1-2e source (with an error of 0.5 subtype). This is consistent with the early-type B star classification proposed in ATel #12229, as well as the previous classification of B0-B3 by Evans et al. (2004, MNRAS, 351, 601; source ID [2dFS]0811).

Thus, we provide the first optical spectrum with Hα emission of the optical counterpart of XTE J0052-723, further confirming its Be/X-ray binary nature.

New paper: Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

Finally after almost a year, our proceedings paper on the B[e] supergiant LHA 120-S 73 is out! It is based on a poster (2015-58aaa-torres-s73) presented on the 58th Annual Meeting of the Argentinian Astronomical Society (La Plata, Argentina, Sep 14-18, 2015) and connected also with our last refereed paper.

Exploring the circumstellar disk-like structure of the B[e] supergiant LHA 120-S 73

Torres A. F., Cidale L., Kraus M., Arias M. L., Maravelias G., Borges Fernandes M., Vallverdú R.

The Large Magellanic Cloud hosts the peculiar B8-type star LHA 120-S 73. Belonging to the B[e] supergiant group, this star is surrounded by large amounts of material which forms a circumstellar disk-like structure, seen more or less pole-on. Within its dense and cool circumstellar disk, molecules form and dust condensates. Based on medium and high-resolution optical and infrared spectroscopic data, we study the structure, kinematics and physical properties of the disk using different tracers, as the emission lines of [Oi] and [Caii] for the innermost gaseous atomic region and the first-overtone bands of CO for the inner border of the molecular disk. We also analyze near-infrared mid-resolution spectra to search for the presence of other molecules and mid-infrared low-resolution spectroscopic observations to study the composition of the dust component.

NASA ADS: 2016BAAA…58..120T

New paper: Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

M. Kraus, L.S. Cidale, M.L. Arias, G. Maravelias, D.H. Nickeler, A.F. Torres, M. Borges Fernandes, A. Aret, M. Cure, R. Vallverdu, R.H. Barba

We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution optical and near-IR spectroscopic data were obtained over a period of 16 and 7 years, respectively. The spectra cover the diagnostic emission lines from [CaII] and [OI], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A low-resolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly non-monotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The mid-infrared spectrum displays features of oxygen- and carbon-rich grain species, which indicates a long-lived, stable dusty disk. We cannot confirm the previously reported high value for the stellar rotation velocity. The line profile of HeI 5876 A is strongly variable in both width and shape and resembles of those seen in non-radially pulsating stars. A proper determination of the real underlying stellar rotation velocity is hence not possible. The existence of multiple stable and clumpy rings of alternating density recalls ring structures around planets. Although there is currently insufficient observational evidence, it is tempting to propose a scenario with one (or more) minor bodies or planets revolving around LHA 120-S 73 and stabilizing the ring system, in analogy to the shepherd moons in planetary systems.

arXiv:1607.00152 | NASA ADS: 2016A&A…593A.112K

New Paper on exoplanets – the SEAWOLF project

Trawling for transits in a sea of noise: A Search for Exoplanets by Analysis of WASP Optical Lightcurves and Follow-up (SEAWOLF)

E. Gaidos, D. R. Anderson, S. Lepine, K. D. Colon, G. Maravelias, N. Narita, E. Chang, J. Beyer, A. Fukui, J. D. Armstrong, A. Zezas, B. J. Fulton, A. W. Mann, R. G. West, F. Faedi

Studies of transiting Neptune-size planets orbiting close to nearby bright stars can inform theories of planet formation because mass and radius and therefore mean density can be accurately estimated and compared with interior models. The distribution of such planets with stellar mass and orbital period relative to their Jovian-mass counterparts can test scenarios of orbital migration, and whether “hot” (period < 10d) Neptunes evolved from “hot” Jupiters as a result of mass loss. We searched 1763 late K and early M dwarf stars for transiting Neptunes by analyzing photometry from the Wide Angle Search for Planets and obtaining high-precision (<10−3) follow-up photometry of stars with candidate transit signals. One star in our sample (GJ 436) hosts a previously reported hot Neptune. We identified 92 candidate signals among 80 other stars and carried out 148 observations of predicted candidate transits with 1-2 m telescopes. Data on 70 WASP signals rules out transits for 39 of them; 28 other signals are ambiguous and/or require more data. Three systems have transit-like events in follow-up photometry and we plan additional follow-up observations. On the basis of no confirmed detections in our survey, we place an upper limit of 10.25% on the occurrence of hot Neptunes around late K and early M dwarfs (95% confidence). A single confirmed detection would translate to an occurrence of 5.3±4.4%. The latter figure is similar to that from Doppler surveys, suggesting that GJ 436b may be the only transiting hot Neptune in our sample. Our analysis of Kepler data for similar but more distant late-type dwarfs yields an occurrence of 0.32±0.21%. Depending on which occurrence is applicable, we estimate that the Next Generation Transit Survey will discover either ~60 or ~1000 hot Neptunes around late K and early M-type dwarfs.