Results 61 to 70 of about 7,097 (207)

Iran's Forward Defense in Sub‐Saharan Africa

Middle East Policy, EarlyView.
Abstract This article examines Iran's security and defense initiatives in sub‐Saharan Africa between 1990 and 2024 and how they reflect the extraterritorial application of the regime's forward defense doctrine. In response to the long‐term erosion of its homeland defense capabilities since the Iran‐Iraq War of the 1980s—driven by infrastructure ...
Ariel Limanya Limbu, Ronen A. Cohen
wiley   +1 more source

Clustering Properties of Intermediate and High-mass Young Stellar Objects

The Astronomical Journal, 2023
We have selected 337 intermediate- and high-mass young stellar objects (YSOs; 1.5–20 M _⊙ ) well-characterized with spectroscopy. By means of the clustering algorithm HDBSCAN, we study their clustering and association properties in the Gaia DR3 catalog ...
Miguel Vioque, Manuel Cavieres, Michelangelo Pantaleoni González, Álvaro Ribas, René D. Oudmaijer, Ignacio Mendigutía, Lena Kilian, Héctor Cánovas, Michael A. Kuhn   +8 more
doaj   +1 more source

Pre-main sequence stars in the Lagoon Nebula (M8) [PDF]

, 2006
We report the discovery of new pre-main sequence (PMS) stars in the Lagoon Nebula (M8) at a distance of 1.25 kpc, based on intermediate resolution spectra obtained with the Boller & Chivens spectrograph at the 6.5-m Magellan I telescope (Las Campanas ...
Arias, Bally, Barbá, Basri, Cieza, Damiani, Drew, Hartigan, Hernández, Hirth, Hirth, J. I. Arias, Jacoby, Kenyon, Kun, Kwan, Lada, Lightfoot, Martín, Martín, Martín, Meyer, Mundt, N. I. Morrell, Palla, Pickles, Prisinzano, R. H. Barbá, Rieke, Skrutskie, Sung, Torres-Dodgen, Tothill, Van Den Ancker, Walker, White   +35 more
core   +4 more sources

The Spectral Variability of the Classical T Tauri Star DR Tauri

The Astronomical Journal, 2001
We present the analysis of 103 spectra, collected over more than a decade, of the classical T Tauri star DR Tau observed with the Hamilton echelle spectrograph at Lick Observatory. The star exhibits strong emission lines that show substantial variety and variability in their profile shapes. The emission lines show signatures of both outflow and infall,
Silvia H. P. Alencar, Christopher M. Johns-Krull, Gibor Basri   +2 more
openaire   +1 more source

Spectropolarimetry of the Classical T Tauri Star TW Hydrae [PDF]

The Astronomical Journal, 2006
We present high resolution (R ~ 60,000) circular spectropolarimetry of the classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines and measure the net longitudinal magnetic field for 6 consecutive nights. While no net polarization is detected the first five nights, a significant photospheric field of Bz = 149 \pm 33 G is found on ...
Yang, H., Johns-Krull, C. M., Valenti, J. A.   +2 more
openaire   +2 more sources

Structure and Computation

Noûs, EarlyView.
ABSTRACT It is a truism of mathematics that differences between isomorphic number systems are irrelevant to arithmetic. This truism is deeply rooted in the modern axiomatic method and underlies most strands of arithmetical structuralism, the view that arithmetic is about some abstract number structure.
Balthasar Grabmayr
wiley   +1 more source

Starspots as an Explanation for the Mysterious IYJ Continuum Excess Emission in Classical T Tauri Stars

The Astrophysical Journal
An accurate estimation of the continuum excess emission from accretion spots and inner circumstellar disk regions is crucial for a proper derivation of fundamental stellar parameters in accreting systems.
Facundo Pérez Paolino, Jeffrey S. Bary, Lynne A. Hillenbrand, Madison Markham, William J. Fischer   +4 more
doaj   +1 more source

Nonradial and nonpolytropic astrophysical outflows IX. Modeling T Tauri jets with a low mass-accretion rate

, 2011
Context: A large sample of T Tauri stars exhibits optical jets, approximately half of which rotate slowly, only at ten per cent of their breakup velocity.
Agra-Amboage, Aibéo, Anderson, André, Bardeen, Beck, Bertout, Blandford, Bouvier, Bouvier, Bouvier, C. Sauty, Cabrit, Cabrit, Calvet, Casse, Choi, Cieza, Clarke, Contopoulos, Decampli, Donati, Dougados, Edwards, Edwards, Fendt, Ferreira, Ferreira, Ferro-Fontán, Garcia, Garcia, Ghosh, Ghosh, Gracia, Gómez de Castro, Gómez de Castro, Günther, Hartigan, Herbst, J. J. G. Lima, K. Tsinganos, Koide, Kopp, Krasnopolsky, Kundurthy, Kwan, Küker, Lavalley-Fouquet, Li, Lima, Marilli, Matsakos, Matsakos, Matt, Matt, Matt, Matt, Matt, Meliani, Mestel, Mestel, Mora, N. Globus, Ouyed, Petrov, Pudritz, Rebull, Rebull, Rebull, Romanova, Sauty, Sauty, Sauty, Sauty, Sauty, Schatzman, Schwartz, Shang, Shu, Spruit, St-Onge, Stassun, Stassun, Stute, Ustyugova, V. Cayatte, Vidotto, Vidotto, Vlahakis, Vlahakis, Walter, Weber, Z. Meliani, Zanni   +93 more
core   +2 more sources

Rotational Evolution of Classical T Tauri Stars: Models and Observations

The Astrophysical Journal
We developed a grid of stellar rotation models for low-mass and solar-type classical T Tauri stars (CTTS; 0.3 M _⊙ < M _* < 1.2 M _⊙ ). These models incorporate the star–disk interaction and magnetospheric ejections to investigate the evolution of the ...
Javier Serna, Giovanni Pinzón, Jesús Hernández, Ezequiel Manzo-Martínez, Karina Mauco, Carlos G. Román-Zúñiga, Nuria Calvet, Cesar Briceño, Ricardo López-Valdivia, Marina Kounkel, Guy S. Stringfellow, Keivan G. Stassun, Marc Pinsonneault, Lucia Adame, Lyra Cao, Kevin Covey, Amelia Bayo, Alexandre Roman-Lopes, Christian Nitschelm, Richard R. Lane   +19 more
doaj   +1 more source

MAGNETOSPHERIC ACCRETION IN T TAURI STARS: OBSERVATIONAL TEST

Odessa Astronomical Publications, 2017
In the classical T Tauri stars (CTTS) the magnetic field plays an important role in the interaction between the star and the accretion disk. In 1996-2000 we have carried out an extensive spectroscopic and photometric monitoring of the extremly active ...
P. P. Petrov
doaj   +1 more source