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Creating OSIRIS mosaic images

To properly process data (either imaging or multi-slit spectra) from the OSIRIS instrument at GTC you need first to convert the original data to single images. The raw fits data contain two extensions corresponding to the two CCD sensors. To combine these into a single 2110 X 2051 pixels image (including the gap between the sensors) they provide with a convenient IRAF script called Mosaic Tool. This takes into account more than simply adding the extensions. As written in the ReadmeFirst.txt file:

(i) corrects the input OSIRIS pre-image for overscan to provide a uniform background, (ii) executes the mosaic assembly according to the rotation/traslation parameters obtained from the MD Polynomial Manual (current version: V5; see contents of the attached MD_polynomials.pdf file) on a new created image, (iii) copies the zero extension of the input image in the new one, and (iv) updates the WCS keywords. Such updating consists in switch the input reference pixel (CRPIX1, CRPIX2) to the center of the mosaic (see MD_polynomials.pdf, p.12) and calculate the celestial coordinates (CRVAL1, CRVAL2) corresponding to the new reference, based on the original WCS parameters. Hence, the correction of the astrometric solution is the same of the input image.

So it does quite a work! To run it you have to start IRAF, define the task and apply it to an raw image:

-->task $mosaic_2x2=mosaic_2x2_v2.cl
-->mosaic_2x2 0002604740-20200628-OSIRIS-OsirisBroadBandImage.fits

(the name for the task, in this case mosaic_2x2 is not really important). When I tried that (using PyRAF v2.1.5 with IRAF 2.16.1 on a Debian 10 machine) I got an error:

Traceback (innermost last):
File "", line 1, in
File "", line 16, in mosaic
AttributeError: Parameter PY not found

which I couldn’t understand. Even after contacting the support the mystery remained. Back in early August we had only a couple of images from our pre-imaging run (and not time to waste…) and the support team was kind enough to do it for us. But now that we have the actual spectroscopic data the images are way too more to ask again for this. Therefore, I tried to search a bit deeper than the first time.

I started by checking the mosaic_2x2_v2.cl file, and I removed all tasks to search where could be the problem. So I edited it to run this:

procedure mosaic (fobjeto)

file fobjeto {"",prompt="Object file:"}


string objeto
file   text





In this form it only calls the basic packages of IRAF. Still though, when I attempted to run it again I took the same error! So the problem was already at the beginning. Then, I noticed these dots after the packages (e.g. noao, noao.artdata.) where obviously python was trying to get a non-existing attribute. After removing these dots it actually proceeded! Only after this revelation, it came to my mind to actually try the IRAF cl directly (when you have the python supported version there is no need to look back to cl!). However, it made a difference as (obviously) the cl doesn’t care about the cots… So the problem was python specific.

The script continued running only to … stuck again:

Traceback (innermost last):
File "", line 1, in
File "", line 44, in mosaic
iraf.imcreate(image = 'CCD_mosaic.fits', naxis = 2, naxis1 = 2110,naxis2 = 2051,pixtype = 'real')
AttributeError: Undefined IRAF task `imcreate'

However, this is easily interpreted. imcreate is a task in the ctio package, which is external (not part of the original core of IRAF). So you need to find the ctio package and put it under the iraf/extern/. This was actually not easy to spot since the support of IRAF by the STScI has dropped and most links are broken. The package is supported by the iraf-community, but I didn’t try to check exactly how to download (as I didn’t find it under my iraf/ directory). On the other hand, I found an alternative (in the iraf.net/forum) using the mkpattern task, under the artdata package which is already loaded in the file. Then, I just replaced the following line:



mkpattern(input="CCD_mosaic.fits",pixtype="real", ndim=2, ncols=2110, nlines=2051)

and all problems are finally solved! The script runs to the end and provides the dinal mosaic image.

Bottomline, or what to do in three single steps

  • If you are running cl/ecl directly AND have ctio package installed you don’t need to do anything
  • If you are running cl/ecl directly and you don’t have ctio, just replace imcreate with mkpattern
  • If you are running on python then remove the dots when the IRAF packages are called

I would therefore strongly suggest the support team to remove the dots and replace the imcreate task so that it can work in all cases.
(For any potential user here is my modified version: mosaic_2x2_v2_gm.cl.txt – remove .txt)

New paper on rho Cas and its recent outburst in 2013

A new outburst of the yellow hypergiant star Rho Cas

Michaela Kraus, Indrek Kolka, Anna Aret, Dieter H. Nickeler, Grigoris Maravelias, Tõnis Eenmäe, Alex Lobel, Valentina G. Klochkova

Yellow hypergiants are evolved massive stars that were suggested to be in post-red supergiant stage. Post-red supergiants that evolve back to the blue, hot side of the Hertzsprung-Russell diagram can intersect a temperature domain in which their atmospheres become unstable against pulsations (the Yellow Void or Yellow Wall), and the stars can experience outbursts with short, but violent mass eruptions. The yellow hypergiant Rho Cas is famous for its historical and recent outbursts, during which the star develops a cool, optically thick wind with a very brief but high mass-loss rate, causing a sudden drop in the light curve. Here we report on a new outburst of Rho Cas which occurred in 2013, accompanied by a temperature decrease of ~3000 K and a brightness drop of 0.6 mag. During the outburst TiO bands appear, together with many low excitation metallic atmospheric lines characteristic for a later spectral type. With this new outburst, it appears that the time interval between individual events decreases, which might indicate that Rho Cas is preparing for a major eruption that could help the star to pass through the Yellow Void. We also analysed the emission features that appear during phases of maximum brightness and find that they vary synchronous with the emission in the prominent [CaII] lines. We conclude that the occasionally detected emission in the spectra of Rho Cas, as well as certain asymmetries seen in the absorption lines of low to medium-excitation potential, are circumstellar in nature, and we discuss the possible origin of this material.

arXiv.org: 1812.03065

New paper on the circumstellar environment of galactic B[e] supergiants

Finally, after some years of work, it has been accepted for publication in MNRAS.

Resolving the kinematics of the disks around Galactic B[e] supergiants

Grigoris Maravelias, Michaela Kraus, Lydia S. Cidale, Marcelo Borges Fernandes, Maria L. Arias, Michel Curé, Georgios Vasilopoulos

B[e] Supergiants are luminous evolved massive stars. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dusty regions usually found in rings or disk-like structures. For a better comprehension of the mechanisms behind the formation of these rings, detailed knowledge about their structure and dynamics is essential. To address that, we obtained high-resolution optical and near-infrared spectra for 8 selected Galactic B[e] Supergiants, for which CO emission has been detected. Assuming Keplerian rotation for the disk, we combine the kinematics obtained from the CO bands in the near-IR with those obtained by fitting the forbidden emission [OI] λ5577, [OI] λλ6300,6363, and [CaII] λλ7291,7323 lines in the optical to probe the disk structure. We find that the emission originates from multiple ring structures around all B[e] Supergiants, with each one of them displaying a unique combination of rings regardless of whether the object is part of a binary system. The confirmed binaries display spectroscopic variations of their line intensities and profiles as well as photometric variability, whereas the ring structures around the single stars are stable.

arXiv.org: 1807.00796

Figure 12 from the paper: A cartoon illustration of the disk-structures as derived from our analysis. We represent the [OI] λ5577 line as *[OI]*, the [OI] λλ6300, 6363 doublet as [OI], and the [CaII] λλ7291, 7323 as [CaII]. The arrows above the rings symbolize the typical ring-widths and are given in km/s. (For more details on the data used and references see Table 3. Note that the relative structures and sizes are not in scale.

IRAF’s identify error – center not found

During the last few days I have struggled a bit with the wavelength calibration of some long-slit spectra. When using the identify task of IRAF I found that I could select (“m”ark) only some of the lines, without any clear indication why the rest were not recognized (some were indeed stronger but others were equal or weaker). The actual error that kept popping out was “Center not found: check cursor position”. Although I went on to investigate all parameters (even the aidpars !) the one thing that solved the problem was finally to increase a bit the full-width of the features to be identified (fwidth), from the default value of 4.0 to 10 pixels. Apparently some of the lines seems too wide to be determined as real features by the task.

New paper on the circumstellar environment of the B[e] supergiant LHA 120-S 35

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Andrea F. Torres, Lydia S. Cidale, Michaela Kraus, María L. Arias, Rodolfo H. Barbá, Grigoris Maravelias, Marcelo Borges Fernandes

B[e] supergiants (SGs) are massive post-main-sequence stars, surrounded by a complex circumstellar (CS) environment. The aim of this work is to investigate the structure and kinematics of the CS disc of the B[e] SG LHA 120-S 35. We used high-resolution optical spectra obtained in different years to model the forbidden emission lines and determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. We also used low-resolution near-infrared (IR) spectra to explore the variability of molecular emission. LHA 120-S 35 displays spectral variability in both optical and IR regions. The P-Cygni line profiles of H I, as well as those of Fe II and O I, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating CS disc. We also observe line-profile variations in the permitted and forbidden features of Fe II and O I. In the IR, we detect variations in the intensity of the H I emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca II] and [O I] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multi-ring structures, revealing density variations along the disc. We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in the Hertzsprung-Russell diagram. The formation of the complex CS structure could be the result of the wind-wind interactions of the post-RSG wind with the previously ejected material from the RSG. However, the presence of a binary companion can not be excluded. Finally, we find that LHA 120-S 35 belongs to a young stellar cluster.

arXiv.org: 1712.09759

New paper: The yellow hypergiant – B[e] supergiant connection

Our most recent work comes as a proceedings paper for the conference “Stars: from collapse to collapse” (Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Cherkessian Republic, Russia, 3-7 October 2016):

The yellow hypergiant – B[e] supergiant connection

A. Aret, M. Kraus, I. Kolka, G. Maravelias

B[e] supergiants and yellow hypergiants share a number of common properties regarding their circumstellar environments. Using the forbidden [O I] and [Ca II] lines as disk tracers, we suggest the presence of a Keplerian disk or ring around the yellow hypergiant V509 Cas and confirm the pole-on inner disk around V1302 Aql. These findings indicate a change in mass-loss behavior from spherical in cooler yellow hypergiants to axisymmetric in the hotter ones during the passage through the Yellow Void. The accumulation of material in the equatorial plane reminds of the disks of B[e] supergiants, supporting the suggestion that yellow hypergiants might appear as B[e] supergiants after they reach the blue edge of the yellow instability domain.

arXiv: 1611.06044

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 Magellanic Supergiants – Disk tracing for B[e] supergiants in the Magellanic Clouds

Disk tracing for B[e] supergiants in the Magellanic Clouds

G. Maravelias, M. Kraus, A. Aret

B[e] supergiants are evolved massive stars with a complex circumstellar environment. A number of important emission features probe the structure and the kinematics of the circumstellar material. In our survey of Magellanic Cloud B[e] supergiants we focus on the [OI] and [CaII] emission lines, which we identified in four more objects.


New Paper on BeXRBs – 5 new BeXRBs in the SMC and the link of the supergiant B[e] star LHA 115-S 18 with an X-ray source

Optical spectra of 5 new Be/X-ray Binaries in the Small Magellanic Cloud and the link of the supergiant B[e] star LHA 115-S 18 with an X-ray source

Grigoris Maravelias, Andreas Zezas, Vallia Antoniou, Despoina Hatzidimitriou

The Small Magellanic Cloud (SMC) is well known to harbor a large number of High-Mass X-ray Binaries (HMXBs). The identification of their optical counterparts provides information on the nature of the donor stars and can help to constrain the parameters of these systems and their evolution. We obtained optical spectra for a number of HMXBs identified in previous Chandra and XMM-Newton surveys of the SMC using the AAOmega/2dF fiber-fed spectrograph at the Anglo-Australian Telescope. We find 5 new Be/X-ray binaries (BeXRBs; including a tentative one), by identifying the spectral type of their optical counterparts, and we confirm the spectral classification of an additional 15 known BeXRBs. We compared the spectral types, orbital periods, and eccentricities of the BeXRB populations in the SMC and the Milky Way and we find marginal evidence for difference between the spectral type distributions, but no statistically significant differences for the orbital periods and the eccentricities. Moreover, our search revealed that the well known supergiant B[e] star LHA 115-S 18 (or AzV 154) is associated with the weak X-ray source CXOU J005409.57-724143.5. We provide evidence that the supergiant star LHA 115-S 18 is the optical counterpart of the X-ray source, and we discuss different possibilities of the origin of its low X-ray luminosity (Lx ~ 4 x 10^33 erg/s).