Archive for November, 2018

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.

The ATel #12224 was released on 17 Nov 2018 (19:01 UT) regarding the identification of the proposed optical counterpart to the source XTE J0052-723 (SXP 4.78; Swift J005139.2-721704) as an Hα emitting OB star. The full text follows.

ATel #12224; G. Maravelias (NOA), V. Antoniou (TTU/SAO), A. Zezas (UoC/SAO), A. Strantzalis (UoA), D. Hatzidimitriou (UoA), F. Haberl (MPE)

on 17 Nov 2018; 19:01 UT /

ATel #12209 reported the detection of a new X-ray transient in the Small Magellanic Cloud (SMC), Swift J005139.2-721704, exhibiting outbursting activity. The system has been classified as a new SMC high-mass X-ray binary based on its identification with the B-type star [M2002]20671. NICER followed up this source immediately (ATel #12219), reporting an absorption-corrected luminosity of LX ~7×1037erg s-1 (0.5-8 keV; 60 kpc). Temporal analysis of NICER and Fermi/GBM observations (ATel #12222) identified Swift J005139.2-721704 with the known X-ray pulsar XTE J0052-723 (SXP 4.78). Evans et al. (2004, MNRAS, 353, 601) obtained a refined B0-3(III) spectral type for [M2002]20671 (= [2dFS]0811) based on optical spectroscopy, but they do not report Hα emission.

Here, we report the identification of the SMC star [M2002]20671, and thus XTE J0052-723, with an Hα emitting source, which confirms XTE J0052-723 as a Be/X-ray binary (Be-XRB) pulsar in the SMC. This source is identified in Hα and R-band observations covering the SMC almost completely (Maravelias et al. 2017, IAUS 329, 373) using the Wide Field Imager on the 2.2m MPG/ESO telescope at La Silla (16/17 November 2011) and the MOSAIC-II camera on the 4m Blanco telescope at Cerro Tololo (15/16 December 2011).

The Hα emitting source is found at RA=00:51:38.78 and DEC=-72:17:04.7 (better than 0.2″ relative astrometry with respect to the 2MASS catalog). It is located 2.2″ away from the Swift position (ATel #12209), with Hα and R-band magnitudes equal to 15.476±0.006 and 15.613±0.008, respectively. The resulting Hα-R color is -0.137±0.010 mag with an SNR~13 above the continuum and an Hα excess significance of ~6σ above the Hα-R baseline value. The only nearby source with significant Hα-R excess is much fainter (Hα and R ~22 mag), has a lower SNR (~4) and is located at a larger distance from the X-ray source (~6″).

Observations with the IMACS f/2 camera on the 6.5m Magellan Telescope (4 October 2004) give B=15.652±0.009 mag and I=15.524±0.017 mag (Strantzalis et al. 2018, IAUS 344, 453; Strantzalis et al. 2019, in prep.), compatible with an OB star.

All the identifications described above secure the nature of Swift J005139.2-721704 = XTE J0052-723 = SXP 4.78 as Be-XRB pulsar in the SMC.

Contributions to the XXXth General Assembly of IAU

Posted November 19, 2018 By grigoris

During the XXXth General Assembly of the International Astronomical Union (in Vienna, Austria) I participated in a number of different meetings. In particular:

1. A poster at the IAU Focus Meeting FM14 on IAU’s role on global astronomy outreach, the latest challenges and bridging different communities (August 23, 2018):

“A paradigm to develop new contributors to Astronomy”

G. Maravelias, E. Vourliotis, K. Marouda, I. Belias, E. Kardasis, P. Papadeas, J. D. Strikis, E. Vakalopoulos, O. Voutyras

One of the most regular activities of amateur clubs is scientific outreach, a paramount chan-
nel to disseminate scientific results. It is typically performed through talks given by both ex-
perts (professional astronomers) and non-experts to a diverse audience, including amateur as-
tronomers. However, this is a rather passive, one-way, approach. The advance of technology
has provided all the tools that can help the audience/amateurs to become more active in the
scientific output. What is often missing is the proper guidance. To address that within the
Greek amateur community the Hellenic Amateur Astronomy Association materialized a train-
ing program (free-of-charge and open-accessed) to develop scientific thought and the practical
capabilities for amateurs to produce valuable results. The program ran from November 2014 to
May 2015 focusing each session (month) to: the Sun, variable stars, comets, planets, artificial
satellites, meteors. A professional and/or an experienced amateur astronomer was leading each
session consisting of a theoretical part (highlights of the field, necessary observational tech-
niques) and a hands-on part (observations and data analysis). At least 50 unique participants
gained significant experience by following parts or the complete program.

arXiv: 1810.04562

2. A talk at the meeting of Division G: Stars and Stellar Physics (August 24 and 27, 2018)

“Rings around B[e] Supergiants”

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

Massive stars affect strongly the insterstellar medium through their intense stellar winds and their rich chemically processed material as they evolve. In specific short-lived transition phases (e.g. B[e] Supergiants, Luminous Blue Variables, Yellow Hypergiants) the mass-loss becomes more enhanced and usually eruptive. This leads to the formation of a complex circumstellar environment, which is not always well understood. To improve our knowledge on these phases we examined the structures found around the B[e] supergiants for a sample of Galactic and Magellanic Cloud sources. Using high-resolution optical and near-infrared spectra, we examine a set of key emission features ([OI], [CaII], CO bandheads) to trace their physical conditions and kinematics in their formation regions. Assuming Keplerian rotation of the circumstellar material we find that each B[e] Supergiant is surrounded by a unique distribution of single and/or multiple equatorial rings. Moroever, we find that these structures seem to be more stable and long-lived around single stars rather than binaries that show significant spectroscopic and photometric variability.

3. A poster at the IAU Symposium 346 on High-mass X-ray binaries: illuminating the passage from massive binaries to merging compact objects (August 27 – 31, 2018)

Clarifying the population of HMXBs in the Small Magellanic Cloud

G. Maravelias, A. Zezas, V. Antoniou, D. Hatzidimitriou, F. Haberl

Almost all confirmed optical counterparts of HMXBs in the SMC are OB stars with equatorial decretion disks (OBe). These sources emit strongly in Balmer lines and standout when imaged through narrow-band Hα imaging. The lack of secure counterparts for a significant fraction of the HMXBs motivated us to search for more. Using the catalogs for OB/OBe stars (Maravelias et al. 2017) and for HMXBs (Haberl & Sturm 2016) we detect 70 optical counterparts (out of 104 covered by our survey). We provide the first identification of the optical counterpart to the source XTEJ0050-731. We verify that 17 previously uncertain optical counterparts are indeed the proper matches. Regarding 52 confirmed HMXBs (known optical counterparts with Hα emission), we detect 39 as OBe and another 13 as OB stars. This allows a direct estimation of the fraction of active OBe stars in HMXBs that show Hα emission at a given epoch to be at least ∼ 75% of their total HMXB population.

arXiv: 1811.10933

And a short note:
I had opted to present the poster works as e-posters, i.e. displayed as an electronic pdf/presentation on interactive monitors which would be placed at each poster halls. The motivation behind this was the fact that the posters could be uploaded before the official start of each session and be available over the whole (two-week) period. But there were some issues:
1. There were only two monitors at each hall, so if somebody else was talking over their poster you had to wait… and wait… and wait… It happened to me that I wanted to show my poster to a colleague but some other people were in front of the monitor for such a long time that it became obvious that it would be easier finally to show it through my laptop.
2. It was not finally that appealing to use as somebody would have to go and see the list of all posters and select each poster to see in detail. In other words you couldn’t browser the posters like what you do when you walk around in the poster session. It would have been much nicer to have the posters rolling somehow randomly in the monitors and continuously to widen their visibility.
3. Interactive it might have been but it was not easy to navigate (e.g. change the session and see another than the active one at that time), while in many cases there were a few bugs (zooming in that resulted in hiding some presentations, or crashing during the slide change).