We spatially and temporally resolve the future Supernova (SN) rate in the Solar vicinity and the whole Galaxy by comparing observational parameters of massive stars with theoretical models for estimating age and mass and, hence, the remaining life-ti
me until the SN explosion. Our SN rate derived in time and space for the future (few Myr) should be the same as in the last few Myr by assuming a constant rate. From BVRIJHK photometry, parallax, spectral type, and luminosity class we compile a Hertzsprung-Russell diagram (H-R D) for 25027 massive stars and derive extinction, and luminosity, then mass, age, and remaining life-time from evolutionary models. Within 600pc our sample of SN progenitors and, hence, SN prediction, is complete, and all future SN events of our sample stars take place in 8% of the area of the sky, whereas 90% of the events take place in 7% of the area of the sky. The current SN rate within 600pc is increased by a factor of 5-6 compared with the Galactic rate. For a distance of 5kpc our sample is incomplete, nevertheless 90% of those SN events take place in only 12% of the area of the projected sky. If the SN rate in the near future is the same as the recent past, there should be unknown young neutron stars concentrated in those areas. Our distribution can be used as input for constraints of gravitational waves detection and for neutron star searches.
The star-forming regions in Chamaeleon (Cha) are among the nearest (distance ~165 pc) and youngest (age ~2 Myrs) conglomerates of recently formed stars and among the ideal targets for studies of star formation. We search for new, hitherto unknown bin
ary or multiple-star components and investigate their membership in Cha and their gravitationally bound nature. We used the NACO instrument at the VLT UT 4/YEPUN of the Paranal Observatory, at 2 or 3 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and Ks band. On the basis of known proper motions and these observations, we analysed the astrometric results in proper motion diagrams to eliminate possible (non-moving) background stars and establish co-moving binaries and multiples. DI Cha turns out to be a quadruple system with a hierachical structure, consisting of two binaries: a G2/M6 pair and a co-moving pair of two M5.5 dwarfs. For both pairs we detected orbital motion (P~130 and ~65 years), although in opposite directions. Sz 22 is a binary whose main component is embedded in a circumstellar disc or reflection nebula, accompanied by a co-moving M4.5 dwarf. CHXR 32 is a triple system, consisting of a single G5 star, weakened by an edge-on disc and a co-moving pair of M1/M3.5 dwarfs whose components show significant variations in their angular separation. Finally, Cha Halpha 5 is a binary consisting of two unresolved M6.5 dwarfs whose strong variations in position angle at its projected separation of only 8 AU imply an orbital period of ~46 years. DI Cha D and Cha Halpha 5 A&B are right at the stellar mass limit and could possibly be brown dwarfs. In spite of various previously published studies of the star-forming regions in Cha we found four hitherto unknown components in young low-mass binaries and multiple systems. (abridged)
We try to constrain the Equation-of-State (EoS) of supra-nuclear-density matter in neutron stars (NSs) by observations of nearby NSs. There are seven thermally emitting NSs known from X-ray and optical observations, the so-called Magnificent Seven (M
7), which are young (up to few Myrs), nearby (within a few hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that we can observe their surfaces. As bright X-ray sources, we can determine their rotational (pulse) period and their period derivative from X-ray timing. From XMM and/or Chandra X-ray spectra, we can determine their temperature. With precise astrometric observations using the Hubble Space Telescope, we can determine their parallax (i.e. distance) and optical flux. From flux, distance, and temperature, one can derive the emitting area - with assumptions about the atmosphere and/or temperature distribution on the surface. This was recently done by us for the two brightest M7 NSs RXJ1856 and RXJ0720. Then, from identifying absorption lines in X-ray spectra, one can also try to determine gravitational redshift. Also, from rotational phase-resolved spectroscopy, we have for the first time determined the compactness (mass/radius) of the M7 NS RBS1223. If also applied to RXJ1856, radius (from luminosity and temperature) and compactness (from X-ray data) will yield the mass and radius - for the first time for an isolated single neutron star. We will present our observations and recent results.
Recently, 60Fe was found in the Earth crust formed in a nearby recent supernova (SN). If the distance to the SN and mass of the progenitor of that SN was known, then one could constrain SN models. Knowing the positions, proper motions, and distances
of dozens of young nearby neutron stars, we can determine their past flight paths and possible kinematic origin. Once the birth place of a neutron star in a SN is found, we would have determined the distance of the SN and the mass of the SN progenitor star.
We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around the world to monitor continuously young (< 100 Myr), nearby (< 1 kpc) stellar clusters mainly to detect young transiting planets (and to s
tudy other variability phenomena on time-scales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e.g. in the first cluster observed, Tr-37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R=16.5 mag with sufficient precision of 50 milli-mag rms (5 mmag rms down to R=14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe 10 similar clusters, we can expect to detect approximately 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90-cm Jena telescope (similar brightness limit, namely within +/-1 mag, for the others) so that planetary transits can be detected. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their time-scales by discovering planets younger than 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (Abstract shortened)
Context: Only two planetary systems around old ms-pulsars are currently known. Young radio pulsars and radio-quiet neutron stars cannot be covered by the usually-applied radio pulse timing technique. However, finding substellar companions around thes
e neutron stars would be of great interest -- not only because of the companions possible exotic formation but also due to the potential access to neutron star physics. Aims: We investigate the closest young neutron stars to search for substellar companions around them. Methods: Young, thus warm substellar companions are visible in the Near Infrared while the neutron star itself is much fainter. Four young neutron stars are moving fast enough to enable a common proper motion search for substellar companions within few years. Results. For Geminga, RX J0720.4-3125, RX J1856.6-3754, and PSR J1932+1059 we did not find any co-moving companion down to 12, 15, 11, 42 Jupiter masses for assumed ages of 1, 1, 1, 3.1 Myrs and distances of 250, 361, 167, 361 pc, respectively. Near Infrared limits are presented for these four as well as five other neutron stars for which we currently have only observations at one epoch. Conclusions: We conclude that young isolated neutron stars rarely have brown dwarf companions.
In our ongoing search for close and faint companions around T Tauri stars, we found a very faint (Ks=14.9mag, Ks_0=14.4mag) object, just ~2.67 northwest of the Chamaeleon star-forming region member CT Cha corresponding to a projected separation of ~4
40AU at 165+/-30 pc. We show that CT Cha A and this faint object form a common proper motion pair from data of the VLT Adaptive Optics (AO) instrument NACO taken in February 2006 and March 2007 and that the companion is by >=4 sigma significance not a stationary background object. Our AO integral field spectroscopy with SINFONI in J, and H+K bands yields a temperature of 2600+/-250K for the companion and an optical extinction of A_V=5.2+/-0.8mag, when compared to spectra calculated from Drift-Phoenix model atmospheres. We demonstrate the validity of the model fits by comparison to several other well-known young sub-stellar objects. Relative flux calibration of the bands was achieved using photometry from the NACO imaging data. We conclude that the CT Cha companion is a very low-mass member of Chamaeleon and very likely a physical companion to CT Cha, as the probability for a by chance alignment is <=0.01. Due to a prominent Pa-Beta emission in the J-band, accretion is probably still ongoing onto the CT Cha companion. From temperature and luminosity (log(Lbol/Lsun)= -2.68+/-0.21), we derive a radius of R=2.20+0.81-0.60 R_Jup. We find a consistent mass of M=17+/-6 MJup for the CT Cha companion from both its luminosity and temperature when placed on evolutionary tracks. Hence, the CT Cha companion is most likely a wide brown dwarf companion or possibly even a planetary mass object.
The R CrA star-forming region has a small dark cloud with quite a number of protostars, T Tauri stars, and some Herbig Ae/Be stars, plus a number of weak-line T Tauri stars around the cloud found by ROSAT follow-up observations. We searched for mul
tiples among the young stars in and around the R CrA cloud in order to investigate multiplicity in this region. We performed interferometric and imaging observations with the speckle camera SHARP I at the ESO 3.5m NTT and adaptive optics observation with ADONIS at the ESO 3.6m telescope, all in the near-infrared bands JHK obtained in the years 1995, 2000, and 2001. We found 13 new binaries among the young stars in CrA between 0.13 arcsec (the diffraction limit) and 6 arcsec (set as an upper separation limit to avoid contamination by chance alignments). While most multiples in CrA are binaries, there are also one quadruple (TY CrA), and one triple (HR 7170) which may form a quintuple together with the binary HR 7169. One of the newly detected companions with a large magnitude difference found near the M3-5 type T Tauri star [MR 81] Ha 17 could be a brown dwarf or an infrared companion with an edge-on disk. Among seven Herbig Ae/Be stars in CrA, six are multiple. The multiplicity frequency in CrA is as high as in similar star forming regions. By comparing with the period distribution of main-sequence stars and extrapolating to separations not probed in this survey, we conclude that the companion-star frequency is 95+/-23 %; i.e. the average number of companions per primary is 0.95.
Neuhaeuser & Comeron (1998, 1999) presented direct imaging evidence, as well as first spectra, of several young stellar and sub-stellar M6- to M8-type objects in the Cha I dark cloud. One of these objects is Cha Halpha 2, classified as brown dwarf ca
ndidate in several publications and suggested as possible binary in Neuhaeuser et al. (2002). We have searched around Cha Halpha 2 for close and faint companions with adaptive optics imaging. Two epochs of direct imaging data were taken with the Very Large Telescope (VLT) Adaptive Optics instrument NACO in February 2006 and March 2007 in Ks-band. We retrieved an earlier image from 2005 from the European Southern Observatory (ESO) Science Archive Facility, increasing the available time coverage. After confirmation of common proper motion, we deduce physical parameters of the objects by spectroscopy, like temperature and mass. We find Cha Halpha 2 to be a very close binary of ~0.16 arcsec separation, having a flux ratio of ~0.91, thus having almost equal brightness and indistinguishable spectral types within the errors. We show that the two tentative components of Cha Halpha 2 form a common proper motion pair, and that neither component is a non-moving background object. We even find evidence for orbital motion. A combined spectrum of both stars spanning optical and near-infrared parts of the spectral energy distribution yields a temperature of 3000+/-100 K, corresponding to a spectral type of M6+/-1 and a surface gravity of log g= 4.0 +0.75-0.5, both from a comparison with GAIA model atmospheres. We derive masses of ~0.110 Msun (>0.070 Msun) and ~0.124 Msun (>0.077 Msun) for the two components of Cha Halpha 2, i.e., probably low-mass stars, but one component could possibly be a brown dwarf.
