@sahars.bsky.social

#astrosci #stellarastro

An infographic explaining the IK Pegasi system. Panel 1 shows the puzzle: a massive white dwarf with a Barium-rich companion. Panel 2 shows the solution: a hierarchical triple system where an inner binary merges. Panel 3 shows the destiny: a double merger leading to a Type Ia Supernova. Infographic created using Gemini.

📢New paper alert!
"IK Pegasi and the Double Merger Path to Type Ia Supernovae", co-led with S. Shahaf
How do you get a massive white dwarf paired with a Barium-rich companion? It started as a triple system!
A potential major pathway to SNe Ia.
ui.adsabs.harvard.edu/abs/2026arXi...
#astronomy #stars

Farewell, Gaia, the best space mission ever. 😢

Forgot to tag! #astronomy #stars

Na'ama Hallakoun on X: "New paper alert! https://t.co/OV5nLY5j5T We identified a significant deficit (of about an order of magnitude!) of massive white dwarfs (WDs) in a volume-complete sample of main-sequence (MS) + WD binary systems, compared to single WDs in the field (i.e. the sky). >> https://t.co/48UTffc300" / X New paper alert! https://t.co/OV5nLY5j5T We identified a significant deficit (of about an order of magnitude!) of massive white dwarfs (WDs) in a volume-complete sample of main-sequence (MS) + WD binary systems, compared to single WDs in the field (i.e. the sky). >> https://t.co/48UTffc300

Nevertheless, we suggest that at least some of these "other" systems might be descendants of triple systems, where the WD in the present-day system is either an unresolved binary consisting of two WDs, or a merger product of such a binary
(see also x.com/ha_naama/sta...).

Finally, the "other" WDs in our sample appear to have lost less mass than isolated WDs, which doesn't make sense. Since these measurements have large uncertainties, it's likely that future, more precise, measurements will place some of them in the "spender" regime. >>

WDs marked as "spenders" have masses that are consistent with WDs that have evolved in isolation, but our initial mass estimates show that they have lost more mass compared to isolated stars, indicating a past mass transfer with their companions. >>

We find that the IFMR of these WDs is significantly different from that of isolated WDs (the black line in this plot).
WDs marked as "low mass" have masses smaller than ~0.4Msun, and could not have formed in isolation in the Galaxy lifetime (massive stars turn into WDs faster). >>

Na'ama Hallakoun on X: "New paper alert! https://t.co/hpmhBpp96N @sahar_shahaf and I, together with Mazeh, Ben-Ami, Rekhi, @kjb_astro and @silvia_toonen found nearly 3,200(!) white dwarf+main sequence astrometric binaries in @ESAGaia DR3 data! >> https://t.co/EiXPs4IroX" / X New paper alert! https://t.co/hpmhBpp96N @sahar_shahaf and I, together with Mazeh, Ben-Ami, Rekhi, @kjb_astro and @silvia_toonen found nearly 3,200(!) white dwarf+main sequence astrometric binaries in @ESAGaia DR3 data! >> https://t.co/EiXPs4IroX

These systems were selected by cross-matching the Gaia
non-single star catalog with published catalogs of stars in open clusters, and applying the selection criteria that we developed in Shahaf+2024 (x.com/ha_naama/sta...), in order to identify binaries with WD companions.>>

While previous studies have studied the IFMR of WDs that have evolved in isolation (without interacting with nearby companions), in this study we focus on WDs that have stellar companions in separations indicating that both stars were close enough to interact in the past. >>

Stellar clusters are large groups of stars, that were formed together at the same time. By examining their properties, we can estimate the age of the cluster. We can then use this estimate to calculate the IFMR of the WDs in this cluster. >>

By subtracting the cooling age from the total age of the star, we can estimate the WD's progenitor mass, based on the theoretical lifetimes of stars of different masses. >>

In order to measure the IFMR, we need to have some indication for the age of the WD. Since WDs cool over time, the temperature of the WD tells us how much time has passed since the star has become a WD (the "cooling age"). >>

WDs are the remnants of stars less massive than 8 times the mass of the Sun (Msun). The relation between the initial mass of the star and the final mass of its WD remnant (aka the IFMR) can tell us a lot about the process governing stellar evolution. >>

New paper alert!
doi.org/10.3847/1538...

In a new paper led by our student, Oren Ironi, we (with Sagi Ben-Ami and Sahar Shahaf) examine the initial-to-final mass relation (IFMR) of white dwarfs (WDs) in binaries with orbital separations of about 1AU. >>

החיסון הוא אותו חיסון לכל הגילאים, המינון לפעוטות הוא חצי מהמינון למבוגרים (שואבים למזרק מאותו בקבוקון).

לבן שנה לא הצלחנו לקבוע תור גם בטלפון, כנראה כי זו מנה ראשונה שלו והמערכת לא מאפשרת לקבוע תור בלי מנה שניה, אז קבעו שני תורים עבורי וחיסנו גם אותו. הצוות לא כל-כך מודע לנהלים (שכנראה גם לא ברורים מספיק), והייתי צריכה להתעקש כדי שיאשרו שהוא צריך גם מנה שניה אחרי 28 יום. >>

התורים לחיסון מאד ספורדיים (יש בערך שעה בשבוע שבה אפשר להתחסן), ובחלק מהמקומות לא ניתן לקבוע תור באינטרנט אלא רק בטלפון (ורק שבוע מראש). >>

***** שירות לציבור, כי נראה שאף-אחד לא שמע על זה: יש חיסונים עדכניים נגד קורונה בקופות החולים, מתאימים החל מגיל חצי שנה. *****

היום התחסנו אני (✅️ מנה #7), בת 4 (✅️ מנה #3), ובן שנה (✅️ מנה #1), בחיסון העדכני (מותאם לוריאנט JN.1) של מודרנא. >>

Thanks!

I'm an astrophysicist working as a staff scientist at the Weizmann Institute of Science.

Yes

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