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We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broadband visual photometry of the O7.5III(n)((f)) star {\xi} Persei in November 2011. This star is well…

The nearby barred spiral galaxy NGC 1672 is thought to have a weak Seyfert nucleus in addition to its strong starburst activity. Observations with the PSPC and HRI instruments on board the ROSAT X-ray satellite show that three X-ray sources…

We present a series of optical spectroscopic and near-infrared photometric observations of the Be star X Persei, from the beginning of the recent emission phase. Our data show that after the latest extended low state (ELS), both the…

The A7 star Altair is one of the hottest magnetically active stars. Its proximity to the Sun allows a detailed investigation of a corona in X-rays for a star with a shallow convection zone. We used a deep XMM-Newton observation of Altair…

We present results of a comprehensive analysis of the X-ray pulsar X Persei over the period 1996 to 2011, encompassing the quite low state and subsequent strong outburst activity. Using data from the RXTE and Swift observatories we detected…

Sirius has always attracted a lot of scientific interest, especially after the discovery of a companion white dwarf at the end of the 19th century. Very early on, the existence of a potential third body was put forward to explain some of…

New Chandra High Resolution Camera pointings on the "non-coronal" red giant Arcturus (HD124897; $\alpha$ Boo: K1.5III) corroborate a tentative soft X-ray detection in a shorter exploratory exposure sixteen years earlier. The apparent source…

Alpha Centauri A is the closest solar-type star to the Sun and offers an excellent opportunity to detect the thermal emission of a mature planet heated by its host star. The MIRI coronagraph on JWST can search the 1-3 AU (1"-2") region…

We analyse a Chandra observation of the rich globular cluster NGC 362, finding 33 X-ray sources within 1' (1.2 half-mass radii) of the cluster center. Spectral analysis of the brightest source (X1) shows blackbody-like emission, indicating…

The Trifid Nebula is a young HII region recently rediscovered as a "pre-Orion" star forming region, containing protostars undergoing violent mass ejections visible in optical jets as seen in images from the Infrared Space Observatory and…

We use X-ray observations of the nearby binaries 61 Cyg A/B (K5V and K7V) and Alpha Cen A/B (G2V and K1V) to study the long-term evolution of magnetic activity in weakly to moderately active G + K dwarfs over nearly a decade. Specifically…

We have made a multiwavelength study of the overlapping error boxes of the unidentified gamma-ray sources TeV J2032+4130 and 3EG J2033+4118 in the direction of the Cygnus OB2 association (d = 1.7 kpc) in order to search for a point-source…

CoRoT-2 is one of the most unusual planetary systems known to date. Its host star is exceptionally active, showing a pronounced, regular pattern of optical variability caused by magnetic activity. The transiting hot Jupiter, CoRoT-2b, shows…

Recent studies of solar-type superflare stars have suggested that even old slowly rotating stars similar to the Sun can have large starspots and superflares. We conducted high dispersion spectroscopy of 49 nearby solar-analog stars (G-type…

AB Dor, Speedy Mic and Rst137B are in their early post-T Tauri evolutionary phase (<100Myr), at the age of fastest rotation in the life of late-type stars. They straddle the coronal saturation-supersaturation boundary first defined by young…

The optical identification of large number of X-ray sources such as those from the ROSAT All-Sky Survey is challenging with conventional spectroscopic follow-up observations. We investigate two ROSAT All-Sky Survey fields of size 10 * 10…

We report the discovery of several new OB/X-ray accreting binary candidates. These massive systems were found by cross-correlating in position SIMBAD OB star catalogues with the part of the ROSAT all-sky survey located at low galactic…

We report the optical identification of the hardest X-ray source (AX J131501+3141) detected in an unbiased wide-area survey in the 0.5--10 keV band, the ASCA Large Sky Survey. The X-ray spectrum of the source is very hard and is well…

Using long-term X-ray observations, we present the short-term and long-term X-ray variability analysis of the ultra-fast rotating active star AB Dor. Flaring events are common in X-ray observations of AB Dor and occupy a substantial portion…

We present a 10-year X-ray light curve and the spectra of a peculiar X-ray transient in the spiral galaxy M81. The source was below the detection limit of ROSAT PSPC before 1993, but it brightened substantially in 1993, with luminosities…