Meeting the APEX research community: Silvia Leurini

We are happy to inaugurate this new space to get to know a bit more our APEX research community. We will be introducing here, through short interviews, some of the most active users of APEX.

They have used the telescope and its instrumentation to progress on their research and achieve interesting scientific results. Many of them have visited the observatory as well, spending good moments in the control room or in from of the moving telescope at the Chajnantor plateau.

They will be telling us a bit about their experiences with APEX, and how relevant has been the use of APEX data for their investigations. Maybe the newest generations of potential APEX users will find here some ideas on how to exploit the potential that APEX offers for the study of the Southern sub-mm sky.

Introducing Dr. Silvia Leurini

Silvia during one of her visits to support commissioning and operations activities at APEX. She appears by one of the huge specimens of Echonopsis atacamensis, on the way up to the Chajnantor plateau.

In this inaugural day will be talking to Dr. Silvia Leurini. She is a full-time researcher at the Osservatorio Astronomico di Cagliari, where she is a member of the Interstellar Medium (ISM) Physics and Star Formation group.

Silvia was born in Rome (Italy) and got her Ph.D. in 2004 at the University of Bonn, working with Prof. K. Menten and Prof. P. Schilke on the dissertation “Methanol: a diagnostic tool for star formation“

After that, she spent three years at ESO as ALMA fellow in Garching, and later moved back to the Max Planck Institut für Radioastronomie in Bonn working as a postdoctoral researcher at the Millimeter and Submillimeter group.

Hi Silvia, we are happy to have you here, inaugurating this section. You are one of the most active APEX users and first author of several publications based on APEX data… when and why did you decide to use APEX for the first time for your research? 

Fig 1. Chemical representation of the Methanol molecule

I first decided to use APEX for my research at the end of my PhD thesis. I was investigating how the methanol molecule (CH3OH), which is often referred to as a weed because it has transitions essentially everywhere along the millimetre and sub-millimetre part of the electromagnetic spectrum, could be turned into a flower, an important tool to understand the physical conditions of the dense ISM where stars form.

This goal can be easily reached by using series of lines in the sub-millimetre, because they cover a broader range of excitation conditions. APEX was about to be opened to the scientific community at that time, and it offered great advantages with respect to other facilities: better site, more combination of receivers, staff at the site to help with the observations, etc.

So, which APEX instruments have you used the most and why were they useful for you?

I am mostly interested in spectroscopy and therefore I essentially used only heterodyne receivers. I think the one I used the most is the CHAMP+ receiver, a 7-pixel heterodyne array working simultaneously at two frequencies (for example, it can observe the CO(6-5) and CO(7-6) transitions at ~ 691 GHz and 807 GHz at the same time).

With the resolution of APEX at these frequencies, CHAMP+ gives the opportunity to map simultaneously two important transitions of CO at an excellent resolution for single dish telescopes, and get information on the distribution of the gas and on its physical conditions. 

Tell us a bit about your experience visiting APEX. Was it useful for you as a scientist to participate from the observations at the observatory?

I am somehow a particular user of APEX because I was post-doc at the Max Planck Institute for Radioastronomy and I came to APEX not only for my own observations but also to support commissioning activities and its operations.

Observing at APEX from the site is an excellent experience: not only the place is beautiful and the staff very helpful, one understands the difficulties of high frequency observations. I think this helped me in better planning my ALMA projects. 

What did you find valuable from that experience, that maybe you had not realised beforehand? How important has been for your line of research and for your career evolution the data you got from APEX? 

My strong involvement in the commissioning of the telescope had profound implications for my career as my direct experience with APEX and high-frequency observations helped in my job search in particular: Immediately after the taking part in the commissioning of APEX, I was selected as ALMA ESO fellow.

Silvia, you are the first author of 11 publications including APEX data. This is an impressive number. Can you highlight the most remarkable scientific results you have obtained with APEX data so far? 

I think there are two results of my research for which I am particularly grateful to APEX.

The first is the detection of a deuterated molecule (DCN, Leurini+ 2006, A&A. 454L, 47) for the first time in a relatively warm environment. This was absolutely unexpected because deuterium fractionation usually happens at low temperatures with H2D+ as main actor. Our detection in a warm environment suggested that deuterium fractionation can happen also in different situations and pointed towards different chemistry pattern.

Fig 2. Spitzer 8 μm image of the molecular complex G351. The white contour is 5% of the C18O (2–1) peak intensity (17.6 K km s−1) integrated in the velocity range − 3.5 ± 0.5 km s−1. The cyan crosses denote the ATLASGAL clumps identified in Leurini et al. 2011, A&A, 533, A85  (and labelled as C1, C2…). The skeleton of G351 and that of the branches is shown by the white dashed line. The B1–B8 labels indicate the eight branches identified in the column density map obtained from the Herschel data. This corresponds to Fig 1 (modified) in Leurini et al. 2019 (A&A, 621A, 130), reproduced with permission.

The second result is related to the infrared dark cloud G351.776-0.527. After my Ph.D., I was using the APEX telescope to investigate massive star forming regions in the southern hemisphere, which, at that time, was quite unexplored.

The IRAS source 17233-3606 immediately showed several interesting characteristics and over the years, I went on studying it and the IRDC in which is hosted in great detail. Since the source is particularly close by for a site of massive star formation (~ 700 pc), it offers the opportunity to study massive star formation at high linear resolution even with a single dish.

IRAS 17233-3606 is one of the first massive star forming regions in which extremely high velocity outflowing gas was detected (Leurini+2009, A&A, 507, 1443L); we detected a low-mass population of young stellar objects along the whole extent of the cloud (Leurini+ 2011, A&A, 533, 85L). The source is hosted in an IRDC which shows a network of filamentary structures which harbour a large reservoir of gas and dust that could still be accreted onto the main structure (Leurini+ 2019, A&A, 621, A130, see Fig. 2). 

As can be seen in Fig. 3, the main filament has a remarkably constant width across its full extent.

Fig 3. SABOCA-250 μm map of G351 (left panel). The white solid line indicates the skeleton of the filament obtained from the NH2 column density map. The map is divided in different regions for the estimate of the filament width along the source. Middle panel: full width at half maximum in arcsec in different regions of the filament. The cross-spine average radial profile of the observed intensity in the SABOCA-350 μm data (black thick line, right panel) is given for three regions (a, b, and c; these are also shown in the other two panels) along G351. The solid red line is the Gaussian fit; the thin black line shows the resolution of the data. The error bars show the dispersion of the measurements in the relative region. This corresponds to Fig 4 (modified) in Leurini et al. 2019 (A&A, 621A, 130), reproduced with permission.

If you would talk to a researcher or student who has never used APEX data in the past, what is, in your experience, the biggest strength of getting APEX data to conduct astronomical research? 

APEX is a modified ALMA prototype antenna. I think APEX should be considered by young researcher as a pathfinder for any research with ALMA at high frequency. It offers the opportunity to get acquainted with problems related to high frequency observations but also to the site, which is the same as that of ALMA.

APEX does not have the resolution of ALMA, but one gets excellent angular resolution compared to other single dishes and at the highest frequencies its resolution is comparable to that of interferometers of older generation. The new generation receivers are very competitive both for spectroscopy and for photometry. I think APEX is an excellent facility to complement ALMA studies. 

Thanks Silvia for your time and for inaugurating this section, and we wish you more successes with APEX and all the best in your future projects!

Silvia’s publications (as first author) with APEX

  • Leurini et al. 2019, Characterising the high-mass star forming filament G351.776-0.527 with Herschel and APEX dust continuum and gas observations, (A&A, 621A, 130L)
  • Leurini et al. 2017, Distribution of water in the G327.3-0.6 massive star-forming region, (A&A, 602A, 70L)
  • Leurini et al. 2015, Spectroscopically resolved far-IR observations of the massive star-forming region G5.89-0.39, (A&A, 584A, 70L)
  • Leurini et al. 2014, SiO excitation from dense shocks in the earliest stages of massive star formation, (A&A, 570A, 49L)
  • Leurini et al. 2013, Evidence of a SiO collimated outflow from a massive YSO in IRAS 17233-3606, (A&A, 554A, 35L)
  • Leurini et al. 2013, The distribution of warm gas in the G327.3-0.6 massive star-forming region, (A&A, 550A, 10L)
  • Leurini et al. 2011, The molecular distribution of the IRDC G351.77-0.51, (A&A, 533A, 85L)
  • Leurini et al. 2009, Extremely high velocity gas from the massive young stellar objects in IRAS 17233-3606, (A&A, 507, 1443L)
  • Leurini et al. 2008, High-mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky, (A&A, 485, 167L)
  • Leurini et al. 2006, APEX 1 mm line survey of the Orion Bar, (A&A, 454L, 47L)
  • Leurini et al. 2006, The high velocity outflow in NGC 6334 I, (A&A, 454L, 83L)