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Astromama with a long-term plan
As told by Conny Aerts

Living in the countryside in the north of Belgium, in a sandy road with hardly any street lights, the stars already attracted my curiosity as a little girl. Growing up in a working-class family meant there was nobody to talk to about science or culture. A pleasant activity in my life at that time was the weekly soccer games played by my two older brothers. I was not allowed to exercise that sport as a girl, which I regretted since I saw the team spirit it involved, and I lacked such a personal experience.

Me at the age of 5

Luckily, the director of the primary (boys) school that I attended – I tend to be an outlier – in our village (Mr. Jef Quirrijnen) noticed my talent for calculus and, knowing my family situation, wanted to discuss with me about the study of my dreams. When I answered him “astronomy” he not only told me to go and study mathematics, but he also went to convince my parents to allow me to go to university “to become a mathematics teacher” instead of forcing me into the technical study of seamstress. I hated sewing… Belgium’s social system offers university studies to anyone with a secondary school diploma, almost free of charge, so there was no concern about that aspect. In the final year of primary school, the director helped me to devise a 10-year plan. I was 12 years old and, given that nobody in the wide family had ever gone to university, I knew I was on my own to turn it into reality.

End of soccer and fights
Most schools in Belgium were still separate for boys and girls at that time, and I had some difficulties to adapt from the primary boys school to the secondary girls school. These girls did not play soccer during the breaks, nor did they fight in physical terms (only with words). I was again an outlier. At age 15 I decided to change secondary school and left the one at 10 km biking from my house. I registered in a school in the city of Antwerp, despite the daily three-hour commute by bike-bus-bus. I had found out it offered an educational track with nine hours of mathematics per week. It turned out to be the perfect school to prepare for undergraduate studies in mathematics, largely thanks to my excellent mathematics teacher, Mrs. Arlette Van Damme.

After secondary school, I became an undergraduate at Antwerp University – it did not offer astronomy as an educational track, but it was the closest and only university I could go to, this time with a 3.5-hour commute per day. The 3rd and 4th year, I managed to shorten the commute time to only three hours per day by biking twice 25 km, except when it snowed – I was in pretty good shape at that time. As the only student – again an outlier – I chose the specialty of mathematical physics during the final year. As such, I got a training in plasma physics and magneto-hydrodynamics. Once graduated at age 22 and supported by my former classmate and meanwhile partner, I applied for a Ph.D. position in Astronomy & Astrophysics at KU Leuven. I was lucky enough to be selected for this six-year assistantship and started earning a living as an astronomer in the fall of 1988. The long-term plan had worked!

“The long-term plan had worked!”

Ph.D. studies changed my life
At KU Leuven, I finally got graduate training in Astronomy & Astrophysics in 1989 and 1990, notably stellar structure and evolution. I learned the theory of stellar oscillations from Professor Paul Smeyers, observational astronomy from my Ph.D. advisor, Professor Christoffel Waelkens, and embarked upon a Ph.D. thesis on the development and application of methods to identify nonradial oscillation modes in massive stars from high-resolution high signal-to-noise (for me that means above 50,000 and 200, respectively) time-series spectroscopy. My Ph.D. studies changed my life quite drastically. All of a sudden, I was allowed to travel by train and airplane instead of bus, bike, and car. I was sent to do weeks-long photometric or spectroscopic observations with telescopes at observatories in Switzerland, Chile (ESO La Silla), and Haute Provence in France, which I thoroughly enjoyed. This international travel and work were the most important eye-openers I ever experienced in my life: it opened the world and brought me in contact with people of different background, colour, and culture. It also finally allowed me to turn the four languages that any Flemish student gets to learn at school into practice. As to this day, I enjoy being a world citizen and travelling became an important aspect of my life, also as a hobby.

“Travelling became an important aspect of my life, also as a hobby.”

Inspiring conference speakers
In 1990, my first attendance to the biennial international pulsation conference brought me to Bologna, by train. It was a great conference and a wonderful experience that I got to meet many of the big names in the field of stellar pulsation. As of then, their papers were backed by a face and also a human story – an important aspect of research for me. One face and science story stood out at that meeting and inspired my future research: I got fascinated by Professor Steve Kawaler, who enlightened the audience with a fabulous review on white dwarfs, including the internal rotation of PG1159+035 deduced from observed splittings of its gravity modes detected thanks to campaigns organised by the Whole Earth Telescope consortium. Steve stressed the importance of preventing interruptions in the data gathering so as to beat frequency aliasing. It was about the only talk I seemed to understand well and it triggered my plan to try and study the internal rotation of massive stars that would later explode as supernova.

The dual career battle
My partner and I both defended our Ph.D. theses in 1993, January and October. No detection of internal rotation had been achieved for a massive star yet. My Ph.D. thesis presented a mathematical method for pulsation mode identification from spectroscopic time series data. The idea of this “moment method” was originally proposed by Luis Balona in 1986. My thesis contained a new version and numerical implementation of this method, as well as its first applications to hot massive pulsators. My Ph.D. defense took place one year ahead of schedule as I was convinced it contained sufficient results to warrant public scrutiny and because I wanted to join my partner (whose Ph.D. scholarship was only four years in duration) while he worked at the Harvard School of Public Health. I was still under contract in Belgium for another year, so aside from living in Boston for a while, I applied and got funding for a two-month research stay with Professor Stan Owocki at the University of Delaware to learn the theory of radiation-driven winds of massive stars. Although we loved living in Boston, we came back to Belgium in 1994, a decision triggered by our pregnancy, by the absence of dual career options (all my job applications in the USA had failed) and, above all, by the too scary outlook of having to deal with the costs of living and daycare in Boston with only one income. Our dual-career project was better treated in Belgium, where my partner got a permanent faculty position while I obtained a competitive three-year junior postdoctoral fellowship of the Research Foundation Flanders (FWO) to perform blue-sky research of my likings and to be organised in my own way. My grant focused on the discovery of hundreds of hot gravity-mode pulsators from the European Space Agency’s Hipparcos satellite, among the impressive zoo of variable stars throughout stellar evolution.

Challenging years
After those three years, FWO offered me a subsequent competitive three-year senior fellowship and it also prolonged my position with about a year to compensate for my two pregnancy leaves – meanwhile we had a daughter and a son. Already back then, FWO dealt with childbirth in an exemplary fashion, thus supporting mothers among their researchers, long before many other funding organisations even had any policy about it. My personal FWO funding covered the period between 1994 and 2001. It allowed me to become the scientist I wanted to be: an astromama and an asteroseismologist with a long-term plan to develop that branch of stellar astrophysics for stars of intermediate and high mass. These seven years of personal FWO funding constituted the perfect bridging phase from my Ph.D. assistantship to the faculty position I occupied at KU Leuven as of 2001, with maximal flexibility to build up international experience at my own and, above all, my family’s pace. Yet, as a young mother at the Institute of Astronomy – again an outlier – my seven years as a postdoc were beyond doubt the toughest period of my career, with two young kids to take care of and no outlook for any permanent academic position. I suffered from physical exhaustion and also mentally from the insecure job situation. It occurred to me that I was doing all the tasks of a faculty member already: lecturing, Ph.D. supervision (of four students), project management, chair of international conferences – notably the pulsation conference I organised in 2001 in Leuven – loads of committee work, etc. I am extremely grateful to the many (often quite more senior) collaborators who agreed to come and visit me in Leuven for joint research rather than me having to travel to them. I still undertook many work trips abroad to gain international experience, but in a format that suited me. The work trips would be short (less than two weeks) in duration as long as our kids were dependent on their parents: one of us would always be working in Belgium to be at home with our children after school closed at 18h. Quite often we as parents crossed each other in an airport or a train station.

“My personal Research Foundation Flanders funding allowed me to become the scientist I wanted to be: an astromama and an asteroseismologist with a long-term plan.”

Working with ESA
While I was still a postdoctoral researcher in 2000, the European Space Agency (ESA) invited me to become a member of the science advisory team for the Eddington space mission project. This opened up the field of space astronomical instrumentation for me and I thoroughly enjoy working with ESA to this day. Bridging engineering and fundamental science with the aim to design, implement, and calibrate space missions for astrophysics, with so many aspects of technology development, economic and industrial return, and equilibria to take care of across all the ESA member states was and still is a fantastic learning experience. It complements and broadens my expertise so as to cover space instrumentation, observations, data analysis, and mathematical modelling. Sadly, the Eddington mission never materialised but I learned how to deal with hard decisions while being active in ESA’s Advisory Structure in the period from 2000 to 2011.

Eureka to help me get through the tough work-life balance
Given the busy times trying to combine dual-academic careers with our family life – with weekly swimming classes on Monday evenings and soccer matches for me to enjoy on Saturdays with my son playing and my daughter as well-organised young team delegate with authority over the teenager boys – it became a tradition to take a two-week end-of-year holiday break. This helped me to catch up on sleep and to slow down from the otherwise daily struggle of an astromama. While I was playing with data during the Christmas break end 2002, beautiful rotational splitting of two nonradial modes of the ßCep star HD129929 popped up in my time-series analysis of its 21-years long light curve gathered with the Swiss telescope in La Silla Observatory in Chile. This data assembly was initiated by my supervisor long before I even started my Ph.D. research. The star’s variability patterns after more than a decade of data gathering were too complex to interpret. Yet I could not resist to keep on monitoring that star ever since my first photometric observing run in Chile. The detection of internal rotation in that massive star was the eureka moment in my career. Together with theoreticians from Université de Liège, we offered the first evidence of non-rigid rotation in a massive star. HD129929 was at that time the only star besides the sun that got such a measurement. The region near its convective core rotates about three times faster than its outer envelope. This star has about 10 times more mass than the sun and so is a supernova progenitor. We had the honour to publish this result in the journal Science.

Cartoons of the interior via the 2 dominant oscillation modes of the star

Cartoons of the interior via the 2 dominant oscillation modes of the star. Figure courtesy by Dr. Pieter Degroote, Leuven, Belgium

It was 2003, almost a decade before the community would get flooded by data from the NASA Kepler space telescope, revealing internal rotation for thousands of stars of intermediate and low mass. My Bologna plan took 13 years to materialize but it had worked!

“The detection of internal rotation in that massive star was the eureka moment in my career.”

Intense lecturing
Years of intense and almost exclusively lecturing occurred from 2001 to 2004, as I had to teach five new courses per year at KU Leuven. In addition, I was also lecturing a first year course in basic astronomy in a duet with Professor Henny Lamers. This weird lecturing constellation resulted from a dedicated action in the Netherlands to put role models in the spotlight, with the aim to get and keep more female students in STEM topics – this was about a decade before the lack of women in STEM became a general point of concern and policy in academia.

Dutch Blitz
Although this Utrecht lecturing task lasted only two months, it was quite a challenge to combine the two days per week working at Utrecht with all my courses in Leuven and the care for our seven- and three-year old kids (our daughter strongly objected!). Yet, it was definitely worth it. Henny gave me many tips on how to lecture to first-year students and also bombarded me with numerous science quiz questions during our discussions on radiation-driven mass loss of hot stars. As a token of appreciation for my Utrecht lecturing with him, he offered me the best present I ever received in terms of balance between minimal cost versus maximal impact: the card game Dutch Blitz. To this day, this remains our favourite family card game when the four of us are together at home, usually with our daughter as winner. Since my Utrecht time, we took that game with us on all our family holidays. So even though I learned a lot about astrophysics and lecturing, Dutch Blitz was definitely the most important outcome of my Utrecht adventure. As if I did not have enough lecturing to do already, I also started a new course of asteroseismology at Radboud University Nijmegen in 2004. This year truly marked a new phase in my career. Thanks to Professor Jan Kuijpers, I became Bijzonder Hoogleraar in Nijmegen, got promoted to Hoogleraar in Leuven, and obtained KU Leuven funding for two so-called concerted research actions, running from 2004-2012. As Prime Investigator, I installed a new international Leuven team, purposefully built upon the principles of diversity and inclusion at a time when nobody in my work environment seemed to care about such aspects of team and people management. KU Leuven’s Institute of Astronomy was too Belgian to my likings so I used the obtained funding to hire postdocs and Ph.D. students coming from abroad, covering both the gender and intro-/extravert axes maximally. Our institute became an international expertise centre in asteroseismology. My long-term FWO postdoc plan had worked!

“Henny gave me the best present I ever received in terms of balance between minimal cost versus maximal impact: the card game Dutch Blitz.”

The book
The years 2006 and 2009 saw the successful launches of the CoRoT and Kepler space missions, delivering uninterrupted high-precision photometric light curves of five-months and four-years duration, respectively. We asteroseismologists knew in advance that this would bring a goldmine for our field of research, although the data was primarily meant for exoplanet hunting – I have always been an advocate of intertwined asteroseismology and exoplanet research. In anticipation of the boom in our field from the new space photometry, I decided to accept Springer’s invitation to write a book on asteroseismology, but only provided that I could invite two co-authors so as to make sure I would learn maximally from the experiment.

Three of us embarked upon a memorable writing project to produce the first monograph on asteroseismology by the time the first CoRoT and Kepler data became public. The book (nicknamed The Bible by some in our community) got finished just in time to help the junior (and perhaps also senior) asteroseismologists with the interpretation of the thousands of new high-cadence high-precision light curves. I hold nothing but fond memories of our intense writing sprints – some in our house so that I could combine the work with the care of our kids. I learned a lot from my two co-authors, Joergen Christensen-Dalsgaard and Don Kurtz, notably about helioseismology, frequency inversions, and on science communication in English (my third language). We were a good author trio, covering most aspects of asteroseismology and being equally picky on the impeccable use of LaTeX.

Gratitude to the ERC
As it happened, the timeframe of the book writing also saw the birth of the European Research Council (ERC), a new, unique, and powerful funding scheme offering large grants for fundamental blue-sky research to anyone with at least two years of postdoctoral experience. Many astrophysicists embraced this great and unique opportunity. In the first competition round back in 2008, I was among the few lucky ones to be awarded a five-year Advanced Investigator grant. The topic of my grant PROSPERITY concerned the probing of the internal physics of stars observed by CoRoT and Kepler, covering as many mass regimes and evolutionary stages as possible. The high-precision space photometry turned our community’s asteroseismology dreams into a daily reality. Asteroseismology became an established and crucial aspect of stellar astrophysics, revealing lots of surprises. Several of my ERC-funded Ph.D. students made major breakthroughs, such as estimation of near-core boundary mixing from gravity modes in stars of intermediate mass from CoRoT light curves and hundred times slower than anticipated core rotation from rotational splitting of so-called mixed modes detected in two-years long Kepler data of evolved red giant stars – successors of our sun and progenitors of white dwarfs. Doppler boosting and oscillations of binary subdwarfs also got developed by my postdocs and Ph.D. students, with swift detections in the one-minute cadence Kepler data. Above all, we had great fun as a team and we never forgot to party and organise team-building days, either with Belgian flavour of excellent food and drinks or with fun travel to conferences.

Developing a new branch in asteroseismology
By 2013, the Kepler light curves were four years long and my junior team members unravelled hundreds of intermediate-mass stars whose rotation frequency is similar to those of their gravity modes. Both the force of gravity and the Coriolis force play an important role to describe nonradial oscillations properly in such a situation and one cannot treat the rotation of the star as a small perturbation in the mathematical description of such gravito-inertial modes. Thanks to my second Advanced Investigator grant, MAMSIE (also my nickname given by my two children), I decided that the time was ripe to develop the new sub-field of gravito-inertial asteroseismology, realising well that it would again be a long-term adventure. We had to educate ourselves in thinking in terms of more complicated mathematical functions to represent the oscillation modes in fast rotators, instead of relying on the well-known spherical harmonics as is fine in slow rotators such as HD129929. This was an excellent time to team up with Professor Stéphane Mathis, expert in the theory of transport processes inside stars working at Saclay, and with Professor Tami Rogers, expert in hydrodynamical simulations at Newcastle. We integrated our three teams in a truly transdisciplinary spirit and started holding biannual brainstorm workshops at Leuven. This allowed us to exploit the Kepler and meanwhile TESS space photometry of hundreds of gravito-inertial pulsators, with thousands of them still to be tackled. The ERC funding has been essential to develop the branch of gravito-inertial asteroseismology and to make the plan work!

“The ERC funding has been essential to develop the branch of gravito-inertial asteroseismology and to make the plan work!”

What’s the next step in asteroseismology?
There is still plenty of development waiting to be done in asteroseismology, whatever the stellar mass regime or evolutionary stage one is interested in. Despite major concerted efforts the past decade by a young and vibrant emerging community, the current theory of stellar structure, evolution, rotation, and oscillations is still unable to explain the space data given the fabulous precision. For me, the next step would be to add additional forces connected with the rotation of stars of intermediate and high mass. Their fast rotation deforms many of these stars appreciably and makes them oblate spheroids rather than spheres as is usually assumed in astrophysics. Moreover, rotating convection induces magnetism. To model a rotating magnetic oblate spheroid properly, we must take the centrifugal and Lorentz forces on board in the modelling tools and this requires a three-dimensional treatment of stellar structure and of the oscillations. So, if we want to be ambitious, we should try and lift asteroseismology from one to three spatial dimensions (3D). Space data to apply 3D asteroseismology is already on our computers for hundreds of stars with identified modes and the application pool will increase tremendously with the ongoing TESS and upcoming PLATO space missions. Developing methodology for 3D asteroseismology would be revolutionary for all fields of astrophysics that rely on stellar models. An endeavour like this will require a concerted and collaborative research initiative intertwining theoretical, numerical, and observational expert teams. It should be a fun and interesting avenue to explore. Who knows such a long-term plan might work one day.

What am I most proud of in my career?
Beyond any doubt, I am most proud of the numerous Ph.D. students and postdocs that I had and still have the privilege to supervise, covering 15 nationalities so far. My inclusive MAMSIE team spirit and personal touch in supervision imply that I got much more out of these bright women and men than they could ever have imagined themselves. Seeing junior researchers grow and become independent scientists gives me the greatest joy and work satisfaction. Most of them have gone on to highly successful careers in STEM, even those that entered my team with a low level or even total lack of self-confidence. My scientific children and grandchildren work in all STEM sectors of our technology-driven society, both in and outside academia. I am particularly proud that several of my former team members have become fabulous STEM teachers, inspiring and educating the next generations on a daily basis in their classrooms. It is extremely rewarding that The Kavli Prize acknowledges my approach to this human aspect of academia by honouring me with this award.

“Seeing junior researchers grow and become independent scientists gives me the greatest joy and work satisfaction.”