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We report the discovery of the ultra-luminous quasi-stellar object SMSS J215728.21−360215.1 with magnitude z = 16.9 and W4 = 7.42 at redshift 4.75. Given absolute magnitudes of M145, AB = −29.3, M300, AB = −30.12, and logLbol/Lbol, ⊙ = 14.84, it is the quasi-stellar object with the highest unlensed UV-optical luminosity currently known in the Universe. It was found by combining proper-motion data from Gaia DR2 with photometry from SkyMapper DR1 and the Wide-field Infrared Survey Explorer. In the GAIA database, it is an isolated single source and thus unlikely to be strongly gravitationally lensed. It is also unlikely to be a beamed source as it is not discovered in the radio domain by either NRAO-VLA Sky Survey or Sydney University Molonglo Southern Survey. It is classed as a weak-emission-line quasi-stellar object and possesses broad absorption line features. A lightcurve from ATLAS spanning the time from 2015 October to 2017 December shows little sign of variability.
We present the first data release of the SkyMapper Southern Survey, a hemispheric survey carried out with the SkyMapper Telescope at Siding Spring Observatory in Australia. Here, we present the survey strategy, data processing, catalogue construction, and database schema. The first data release dataset includes over 66 000 images from the Shallow Survey component, covering an area of 17 200 deg2 in all six SkyMapper passbands uvgriz, while the full area covered by any passband exceeds 20 000 deg2. The catalogues contain over 285 million unique astrophysical objects, complete to roughly 18 mag in all bands. We compare our griz point-source photometry with Pan-STARRS1 first data release and note an RMS scatter of 2%. The internal reproducibility of SkyMapper photometry is on the order of 1%. Astrometric precision is better than 0.2 arcsec based on comparison with Gaia first data release. We describe the end-user database, through which data are presented to the world community, and provide some illustrative science queries.
One of the major science goals of the SkyMapper survey of the Southern Hemisphere sky is the determination of the shape and extent of the halo of the Galaxy. In this paper, we quantify the likely efficiency and completeness of the survey as regards the detection of RR Lyrae variable stars, which are excellent tracers of the halo stellar population. We have accomplished this via observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for single-epoch uvgri observations followed by two further epochs of g, r imaging, as per the intended three-epoch survey strategy, we recover known RR Lyraes with a completeness exceeding 90%. We also investigate boundaries in the gravity-sensitive single-epoch two-colour diagram that yield high completeness and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the general usefulness of this diagram in separating populations.
This paper presents the design and science goals for the SkyMapper telescope. SkyMapper is a 1.3-m telescope featuring a 5.7-square-degree field-of-view Cassegrain imager commissioned for the Australian National University's Research School of Astronomy and Astrophysics. It is located at Siding Spring Observatory, Coonabarabran, NSW, Australia and will see first light in late 2007.
The imager possesses 16 384 × 16 384 0.5-arcsec pixels. The primary scientific goal of the facility is to perform the Southern Sky Survey, a six-colour and multi-epoch (four-hour, one-day, one-week, one-month and one-year sampling) photometric survey of the southerly 2π sr to g ∼23 mag. The survey will provide photometry to better than 3% global accuracy and astrometry to better than 50 milliarcsec. Data will be supplied to the community as part of the Virtual Observatory effort. The survey will take five years to complete.
We started a systematic search for periodic variable-star candidates in the EROS-2 database in the context of preparatory work for the Gaia satellite mission. The goal is to evaluate different classification tools and strategies, and to identify a large sample of variable candidates. In this paper we present the results of an assessment study of a three-step identification and classification process. In the study we took a sample of about 80,000 stars from one of the LMC EROS fields.
The optimal sinusoidal excitation of an ultrasonic transducer requests a
knowledge of the frequency and the impedance of the used ceramic. These
parameters, that vary during the application, depend on the characteristics
of the transducer but also on the acoustic load of the propagation medium.
In the search for an adaptive excitation, we propose the design of a digital
generator assuring the functions of automatic tuning and impedance matching.
The design uses the Butterworth-Van Dycke model of pizoelectric ceramics.
The method of determination and identification of the model parameters is
presented and applied on three different transducers.
The negative feedback of the generator is carried out by the signal measured
on the transducers. The dynamic voltage being very variable, the output
resistor of the driver is controlled by transducer impedance.
This feedback control allows the stability of the output voltage to a
constant value whatever the frequency and the medium is.
A Simulink® model of the regulation loop shows that the
frequency tuning could be realized by exploiting the command signal of the
driver resistance. The precision and the stability of the feedback system
are tested for frequencies between 1 to 3 MHz.
The nature and the location of the lenses discovered in the microlensing surveys done so far towards the LMC remain unclear.
This contribution is comprised of two distinct parts. In the first part, motivated by these questions, we compute the optical depth for the different intervening populations and the number of expected events for self-lensing, using a recently drawn coherent picture of the geometrical structure and dynamics of the LMC disk. By comparing the theoretical quantities with the values of the observed events it is possible to put some constraints on the location and the nature of the machos. Clearly, given the large uncertainties and the few events at our disposal it is not yet possible to draw sharp conclusions, nevertheless we find that up to 3-4 macho events might be due to lenses in LMC, which are most probably low mass stars, but that hardly all events can be due to self-lensing. A plausible solution is that the events observed so far are due to lenses belonging to different intervening populations: low mass stars in the LMC, in the thick disk, in the spheroid and some true machos in the halo of the Milky Way and the LMC itself. We report also on recent results of microlensing searches in direction of the M31 galaxy, by using the pixel method. The present analysis still does not allow yet to draw sharp conclusions on the macho content of the M31 galaxy.
In the second part (section 5), a preliminary account of the final results from the EROS-2 programme is presented. Based on the analysis of 33 million LMC and SMC stars followed during 6.7 years, strict limits on the macho content of the galactic halo are presented; they cover the range of macho masses between 0.0001 and 100 solar mass. The limits are better than 20% (resp. 5%) of the standard halo for masses between 0.0002 and 10 (resp. 0.001 to 0.1) solar mass. This is presently the data set with the largest sensitivity to halo machos.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
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