Journals
2025 EN
Camisassa Maria
ABSTRACT White dwarf stars are the most common endpoint of stellar evolution. Therefore, these old, numerous and compact objects provide valuable information on the late stages of stellar evolution, the physics of dense plasma and the structure and evolution of our Galaxy. The ESA Gaia space mission has revolutionized this research field, providing parallaxes and multi‐band photometry for nearly 360,000 white dwarfs. Furthermore, this data, combined with spectroscopical and spectropolarimetric observations, have provided new information on their chemical abundances and magnetic fields. This large data set has raised new questions on the nature of white dwarfs, boosting our theoretical efforts for understanding the physics that governs their evolution and for improving the statistical analysis of their collective properties. In this article, I summarize the current state of our understanding of the collective properties of white dwarfs, based of detailed theoretical models and population synthesis studies.
WILEY‐VCH Verlag GmbH & Co. KGaA
Journals
2025 EN
Di Marco Alessandro
ABSTRACT The Imaging X‐ray Polarimetry Explorer, recently awarded by the American Astronomical Society with the Bruno Rossi prize, observed several accreting neutron stars in X‐ray binaries during the first 2 years of its prime mission. Results obtained for weakly magnetized neutron stars allow us to model the geometry and the physical status of the different emitting regions (accretion disk, boundary/spreading layer) in a completely novel way, showing a more intricate scenario with respect to the one initially anticipated based on theoretical models. In particular, polarization measurements have demonstrated variations with energy and time, which are highly intriguing. Here, a summary of the IXPE findings for these sources, in particular 4U 1820–303, and Cir X–1 are reported.
WILEY‐VCH Verlag GmbH & Co. KGaA
Journals
2025 EN
Mugrauer Markus · Kollak AnnKathrin · Pietsch Lara
+1 more
ABSTRACT In this paper, we present the latest results of our ongoing multiplicity survey of (Community) TESS Objects of Interest, using astrometry and photometry from the latest data release of the ESA Gaia mission to detect stellar companions of these stars and to characterize their properties. A total of 92 binary and two hierarchical triple star systems are identified among the 745 target stars whose multiplicity is explored in this study, all at distances of less than 500 pc around the Sun. As expected for components of gravitationally bound star systems, the targets and the detected companions are at the same distance and share a common proper motion, as shown by their accurate Gaia astrometry. The companions have masses of about 0.12 to 1.6M ⊙ $$ {M}_{\odot } $$ and are most frequently found in the mass range up to 0.6M ⊙ $$ {M}_{\odot } $$ . The companions have projected separations from the targets between about 110 and 9600 au. Their frequency is highest and constant from about 300 to 800 au, decreasing at larger projected separations. In addition to main sequence stars, five white dwarf companions are detected in this study, whose true nature is unveiled by their photometric properties.
WILEY‐VCH Verlag GmbH & Co. KGaA
Journals
2025 EN
Ness JanUwe · Schartel Norbert · SantosLleo Maria
ABSTRACT XMM‐Newton is an ESA space x‐ray observatory launched on 11 December 1999, and after 25 years, a study is presented demonstrating that the data of the mission are efficiently used by an engaged and productive community. The total number of refereed papers published between 2000 and 2024 is 8486. These papers have a total of 15,627 different authors, including 3292 unique first authors. The total available science time during this period amounts to 556 Ms (16,894 observations) 87% of which (84% of observations) have been used in at least one refereed publication, excluding primary catalogue papers. Accounting for multiple use, the observation time has been over‐used by a factor of up to 15 in dedicated publications and even a factor of up to 30 when including a small fraction of papers classified as survey/catalogue. The speed with which observations are published for the first time peaks around 2 years and is thus longer than the proprietary period for Guest–Observer (GO) observations. A strong secondary peak at 3 years suggests that data not published by the proposing teams are picked up by the community, then also taking about 2 years to be published. The publication rate remains stable at∼ 400 $$ \sim 400 $$ refereed articles per year with a small increase in recent years, owed to an increased use of primary XMM‐Newton catalogues. 95% of articles focus on specific data using< 49 $$ <49 $$ observations while 99% of articles use less than 239 observations. Since 2010, the annual number of first‐time authors has remained relatively constant, equalling the number of last‐time authors. This implies that the number of scientists engaged in research utilising XMM‐Newton data has remained constant at 4300, of whom 570 are lead (first) authors. A histogram of the activity period demonstrates that 51% of first authors publish for only 1 year, 24% of first authors are active for up to 6 years, and 25% were active for more than 6 years. We further identify a highly productive core community of approximately 120 scientists publishing an XMM‐Newton article at least every 2 year as first authors. When all authors are considered, the figures are 40%, 25% and 35%, respectively. The considerable number of time‐limited activities may reflect a high level of utilisation during the early stages of a research career, from Master's studies through the PhD and initial postdoctoral years. The trends assessed indicate a vital community with positive perspectives and a continued, active interest in XMM‐Newton for the future.
WILEY‐VCH Verlag GmbH & Co. KGaA
Journals
2025 EN
For most nonprofit leaders and their boards, an annual retreat can help them to foster interpersonal relations, build group cohesion and help them to renew their commitment to the organization and its mission.
Journals
2025 EN
Nonprofits looking for an easy way to bolster effective governance in their organizations should consider drafting a formal board agreement for new and existing board members to sign. But experts caution against adopting generic templates for such agreements. Instead, they should proceed with an understanding that each nonprofit has a unique structure, culture and mission, which makes a one‐size‐fits‐all board agreement challenging—and likely, ineffective.
Journals
2025 EN
Are your board meetings running too long, relying on too many lengthy presentations from staff? If so, you may want to try a flipped meeting agenda, a new approach gaining ground among mission‐driven organizations.
Journals
2025 EN
It's true that with all presidential transitions there's a certain level of uncertainly and change as new agendas take funding priority. But it's fair to say that the rollout of the second Trump Administration's agenda brought an unprecedented level of chaos and unpredictability for any individual and group with even the most tenuous ties to federal funding, sending many in the nonprofit world into a tailspin as money—often, funds already doled out and committed to programming—was apparently rescinded. Even after courts stepped in and called a temporary stop to announced funding freezes, many recipients still struggled to access money they had every reason to expect to flow—leading to even greater confusion.
Journals
2025 EN
While nonprofit boards often seek out new recruits with notable professional experience, wide (and preferably affluent) social circles and varied political and sociological perspectives, that doesn't necessarily mean they will be fluent in the organization's mission, program areas and the more specific details of board service.
Journals
2025 EN
Research suggests that most nonprofit organizations struggle with bringing their new board members up to speed quickly and effectively through a solid onboarding process. In fact, some studies show that as much as a quarter of board members don't have a solid understanding of their organization's mission or strategy—the most basic starting point for good governance and decision‐making. Experts say that's due to another survey findings—just about half of nonprofits have any formal onboarding process in place at all for new members—and many of those that do report poor results.