iiinova — where your digital self keeps evolving

Stay tuned for more. There is a whole range of possible configurations that may explode as supernovae Ia. We have produced 10,000s models to explore every configuration. This will produce predictions for every evolutionary step on the way which can be tested with current and upcoming sky surveys 🔭🧪

Whats the coolest about this? We cannot only tell the full story of a supernova Ia progenitor but 1) we can estimate the efficiency of the common envelope for this system 2) we can now try to find systems at earlier stages, e.g. main sequence binaries or hot subdwarfs with a red giant companion 🔭🧪

This picture shows the common envelope efficiency as a function of orbital period, showing that. a high common envelope is needed for this system

The CE removes a huge amount of angular momentum from the binary and shrinks the orbit to an orbital period of only 95min. At this point gravitational wave radiation drives the evolution and shrinks the orbit further until the binary reaches an orbital period of 76min. where we observe it today 🔭🧪

This is a table which provides details for each evolutionary step of the binary

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After another ~100Myrs the companion has evolved off the main sequence, finished helium core burning and ascended on the asymptotic giant branch. When the companion reaches a radius of ~62 Rsun, it fills its Roche Lobe and a 2nd phase of mass transfer starts - a common envelope (CE) forms 🔭🧪

There are two pictures which show the evolution of the star with then forms a white dwarf prior (left) and post (right) common envelope

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Mass transfer continues for about 10Mys where the star loses almost its entire hydrogen envelope and is left as a so-called hot subdwarf star, while the orbit has widened to ~150 days. The companion has gained a significant fraction of the mass and continues to evolve on the main sequence 🔭🧪

This upper picture shows the mass transfer rate during the first phase of mass transfer. The lower picture shows the change in mass of the donor star during mass transfer

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Here is how it went. The system started as main sequence binary with almost equal masses ~2.6 Msun at an orbital period of ~3 days. The more massive star evolves first and once reaching the subgiant phase, fills its Roche Lobe and starts conservative mass transfer to the main sequence companion 🔭🧪

This picture shows the full evolution of the hot subwarf progenitor in an Hertzsprung Russell diagram from main sequence to current day observations

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Thomas Kupfer @thomkupfer.bsky.social · 26/03/2026

There are only a handful supernova type Ia progenitor systems known. But one of them, PTF1 J2238, has properties measured precise enough to trace back the time and understand how the system formed. Stephania Hernandez, a Postdoc in my group, led a study to explain the full history of the system 🔭🧪

The image shows the cover page of the paper by Hernandez et al. including the title and the abstract

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He just gave his progress report and will finish his MSc thesis later this year. So, now the best part, if you are looking for an amazing PhD student who knows binary evolution, large spectroscopic surveys, transients etc. he is still looking for a PhD position.

The picture shows Vishaak standing in the library of the Hamburg observatory, next to his final slide of his progress report

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Thomas Kupfer @thomkupfer.bsky.social · 26/03/2026

Once in outburst he submits the object to SDSS-V for identification, with the goal to find a rare helium CV - a so called AM CVn binary. Although, so far all observed objects are regular hydrogen-rich CVs, he is testing the capabilities of this new ToO mode and provides lots of interesting feedback

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Thomas Kupfer @thomkupfer.bsky.social · 26/03/2026

@sdssurveys.bsky.social is pioneering ToO observations with a large scale multi-object spectroscopic survey. For the first time we use a MOS survey to identify transients. My MSc student, Vishaak Balasubramanya, is monitoring >10,000 accreting white dwarfs with ZTF and in the future LSST

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Thomas Kupfer @thomkupfer.bsky.social · 25/02/2026

If you are interested, we submitted white papers about this topic to the recent call of white papers from @eso.org to address the question "What science questions will astronomy need to answer in the 2040s" which is part of their Expanding horizons program 🔭

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Thomas Kupfer @thomkupfer.bsky.social · 25/02/2026

Well, what you need is one or more arrays of small to medium-size telescopes which can take spectra with no readout penalty independently from each other or combined as a large array acting as single telescope. 🔭

Thomas Kupfer @thomkupfer.bsky.social · 25/02/2026

How can we best observe the most compact binaries with orbital periods as short as a few minutes, close to their final merger? They are strong supernova Ia progenitor candidates crucial to cosmology and are the strongest Galactic gravitational wave sources in the @lisacommunity.bsky.social regime 🔭

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This was a very successful study making use of high quality HST UV spectra and is only the first in a series of several. HST has observed a dozen AMCVns which will give us enough statistics to solve the puzzle what are the donor stars in AMCVns. Stay tuned for more exciting work from Will. (7/7) 🔭

We also found a higher accretor temperature than previous studies and a rather massive accreting white dwarf. If that holds for other systems that means that their gravitational wave signal will be stronger than previously thought with more typical white dwarf masses. (6/7) 🔭

Most importantly, we found a strong enhancement of nitrogen, which points to CNO processed material in the donor which is currently being transferred to the accretor. This points to either a white dwarf donor or a system that has evolved from a regular CV; we can exclude a He-star donor (5/7) 🔭

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That is exactly what Will has done. We took UV spectra with the Hubble Space telescope (HST) of this benchmark AMCVn to study the spectral features, measures abundances and properties of the accreting white dwarf. We found features of elements such as nitrogen, silicon, iron, or aluminium (4/7) 🔭

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Despite their importance, we have no idea what the donors are, besides that they are helium rich. The accreting white dwarf and accretion disc outshine the donor. So we have to use a trick and observe the material that has been transferred to the accreting white dwarf from the donor. (3/7) 🔭

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AMCVn binaries are ultracompact accreting white dwarfs which are important as supernova Ia progenitors, @lisacommunity.bsky.social gravitational wave sources and mark the end point of binary evolution.They are extreme in many ways and can reach orbital periods as short as 5min (2/7) 🔭

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Thomas Kupfer @thomkupfer.bsky.social · 19/09/2025

Congratulations to my PhD student Weitian (Will) Yu @uni-hamburg.de for his first 1st author paper: arxiv.org/pdf/2512.04147 He did the first detailed abundance analysis of an ultracompact AMCVn binary ZTFJ2252-0519. What did we learn from this analysis (1/7) 🔭

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A big thank you also to Martin M. Roth for giving us a quick tour of the Zentrum für Technologieentwicklung (ZTE). I can only say: Very impressive! @uni-hamburg.de

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Thomas Kupfer @thomkupfer.bsky.social · 19/09/2025

The conference was held in the Synagogue Kulturzentrum; one of the most beautiful buildings I had ever given a presentation. Deutsches Zentrum für Astrophysik congratulations to a great conference!

Thomas Kupfer @thomkupfer.bsky.social · 19/09/2025

I had so much fun presenting our @eso.org Expanding horizons idea for the Time Domain Telescope and its connection to multi-messenger astrophysics at the @germanastrosoc.bsky.social meeting organized by the Deutsches Zentrum für Astrophysik in the really pretty town Görlitz. 🔭🧪

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Thomas Kupfer @thomkupfer.bsky.social · 18/09/2025

Thanks a lot for organizing a great town hall about the different ideas for the ESO Expanding horizons program 🔭

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Thomas Kupfer @thomkupfer.bsky.social · 03/09/2025

We also had the opportunity to spend some fun hours together and even show the team parts of the beautiful city of Hamburg @uni-hamburg.de

Thomas Kupfer @thomkupfer.bsky.social · 03/09/2025

This week we welcomed the BlackGEM collaboration for a team meeting at Hamburg Observatory. We had lots of exciting science presentations and many fruitful conversations about the amazing science we already have been doing with BlackGEM and will be doing in the future.

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Thomas Kupfer @thomkupfer.bsky.social · 29/08/2025

We also had to say goodbye to two amazing RISE students, Bennett Kirby and Isabel Jackson, who spend the summer in Hamburg working with us on radial mode pulsators and supernova Ia progenitors @uni-hamburg.de

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Thomas Kupfer @thomkupfer.bsky.social · 29/08/2025

Three weeks ago my close collaborator and friend Brad N. Barlow came to visit us at the observatory with one of his graduate students. We had a great collaboration meeting with lots of inspiring discussions!

Group picture of the research group of Prof. Kupfer in front of the main building at Hamburg Observatory

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Thomas Kupfer @thomkupfer.bsky.social · 23/07/2025

Looking Forward to great 3 day visit at @maxplanck.de for Astrophysics to give the Joint Astro Colloquium.

Picture shows the front of the Max Planck Institute of Astrophysics

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Thomas Kupfer @thomkupfer.bsky.social · 29/01/2025

Today, we had a very inspiring Colloquium on the incredible things we will be able to do with @lisacommunity.bsky.social Valeriya certainly sparked lots of interest about the mission here at Hamburg observatory

The picture shows the presenter giving the talk in the historic library at Hamburg observatory

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Thomas Kupfer @thomkupfer.bsky.social · 28/01/2025

I am looking for a PhD student to join us at Hamburg observatory to work on compact binaries, LISA sources and supernova Ia progenitors. The position is funded through my ERC starting grant. Application deadline is February 28th and you can apply follow the link: www.uni-hamburg.de/stellenangeb...

uni-hamburg.de

Ausschreibung

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Thomas Kupfer @thomkupfer.bsky.social · 13/01/2025

I'm a Professor of Astronomy at the university of Hamburg. I work on compact binaries, LISA sources, Supernova progenitors and large scale surveys.

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The second project is offered by my student Eric Stringer and the goal is to do kinematic studies of the known compact sdB+WD systems to understand their Galactic kinematics (thin disc, thick disc, halo). www.rise-germany.de/offer/offers...

rise-germany.de

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The first project is offered by my student Corey Bradshaw and the goal is to use TESS data to search for companions of BLAPs and radial mode sdB pulsators by doing timing measurements of the pulsations. www.rise-germany.de/offer/offers...

rise-germany.de

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We have two projects in my group. The project descriptions are attached and the links to the applications are given below. Application deadline is November 30th.

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Thomas Kupfer @thomkupfer.bsky.social · 10/10/2024

Students from North American, British and Irish universities, here is something for you. The RISE program provides funding for a summer internship at a German research institute. See here for more details: www.daad.de/rise/en/rise...

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I am excited that I am part of the Definition Committee for the Galactic Plane Survey. If you have ideas for a survey strategy to conduct interesting science in the Galactic Plane, we are still collecting pitches or white papers. Just follow the instructions here: roman.gsfc.nasa.gov/science/gala...

roman.gsfc.nasa.gov

Nancy Grace Roman Space Telescope

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Thomas Kupfer @thomkupfer.bsky.social · 10/10/2024

Following a recommendation from the Early-Definition Astrophysics Survey Assessment Committee, the Nancy Roman Space telescope will conduct a community-defined Galactic Plane General Astrophysics Survey, of up to approximately 700 hours.

roman.gsfc.nasa.gov

Nancy Grace Roman Space Telescope

The images show the photometric measurements for this object taken with the Oskar Luehning Telescope. The dips occur when one object of the binary moves in front of the other component which happens on a regular binary period of 39 minutes. Cluster of Excellence Quantum Universe

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This source is also expected to be directly dected in gravitational waves by LISA - a future large ESA mission measuring gravitational waves from space.

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@uni-hamburg.de Master student Paul Teckenburg took data of a gravitational wave source with the Oskar Luehning Telescope located at Hamburg Observatory in Hamburg-Bergedorf. With this data he is able to measure the orbital decay of the system and predict its gravitational wave strength.

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