1,725,676 research outputs found
NGC 7793
No full textEsta imagem real, advinda de satélite, mostra a Galáxia NGC 7793, a aproximadamente 10 milhões de anos-luz do planeta TerraComponente Curricular::Educação Superior::Ciências Exatas e da Terra::AstronomiaComponente Curricular::Educação Superior::Ciências Exatas e da Terra::Físic
NGC 7793
No full textEsta imagem real, advinda de satélite, mostra a Galáxia NGC 7793, a aproximadamente 10 milhões de anos-luz do planeta TerraComponente Curricular::Educação Superior::Ciências Exatas e da Terra::AstronomiaComponente Curricular::Educação Superior::Ciências Exatas e da Terra::Físic
NGC 7793
No full textEsta imagem real, advinda de satélite, mostra a Galáxia NGC 7793, a aproximadamente 10 milhões de anos-luz do planeta TerraComponente Curricular::Educação Superior::Ciências Exatas e da Terra::AstronomiaComponente Curricular::Educação Superior::Ciências Exatas e da Terra::Físic
Estudio interferencial de NGC 7793
No full textObservaciones interferenciales han permitido establecer la estructura geométrica y cinemática de NGC 7793, que resulta una galaxia enana de baja densidad.Asociación Argentina de Astronomí
A new candidate pulsating ULX in NGC 7793
No full textInternational audienceWe report here the discovery of NGC 7793 ULX-4, a new transient ultraluminous X-ray source (ULX) in NGC 7793, a spiral galaxy already well known for harbouring several ULXs. This new source underwent an outburst in 2012, when it was detected by \textit{XMM-Newton} and the \textit{Swift} X-ray telescope. The outburst reached a peak luminosity of 3.4 erg\ s and lasted for about 8 months, after which the source went below a luminosity of erg\ s; previous \textit{Chandra} observations constrain the low-state luminosity below 2 erg\ s, implying a variability of at least a factor 1000. We propose four possible optical counterparts, found in archival HST observations of the galaxy. A pulsation in the \textit{XMM-Newton} signal was found at 2.52 Hz, with a significance of , and an associated spin-up of Hz.s. NGC 7793 is therefore the first galaxy to host more than one pulsating ULX
New X-ray supernova remnants in NGC 7793
No full textContext. This work focuses on the detection of X-ray supernova remnants (SNRs) in the galaxy NGC 7793 and the study of their properties.
Aims. X-ray SNRs in galaxies beyond the Local Group are rare, mainly due to the limited sensitivity of current X-ray instruments. Additionally, their identification requires an optical counterpart, making incomplete optical identification methods an extra challenge. Detecting X-ray SNRs in other galaxies is crucial to understanding their feedback in different evolutionary phases and gaining insights into their local interstellar medium (ISM). In NGC 7793, only one X-ray SNR was previously known, while a recent study reported nearly 240 optical SNRs. The discovery of a new, larger optical SNR sample motivated a re-examination of the X-ray SNR population by comparing optical SNRs with X-ray sources.
Methods. To identify X-ray SNRs, we utilised Chandra’s spatial resolution and analyzed all available archival data of NGC 7793, totaling 229.9 ks over 19 years. After data reduction, we performed source detection and analysis, searching for X-ray sources coinciding with optical SNRs. We also used XMM-Newton (1.1 Ms combined EPIC MOS) for a spectral analysis of the confirmed and candidate SNRs.
Results. We detected 58 X-ray sources down to an observed luminosity of ∼9 × 1035 erg s−1. Among them, five X-ray counterparts to optical SNRs were identified, all presenting soft emission (< 1.2 keV) with no short- or long-term variability. One corresponds to the previously known X-ray SNR, while four are newly detected. Spectral modelling of two SNRs shows thermal spectra exceeding 2.5 million K, with strong O VII, O VIII, and Ne IX emission lines. A correlation between density, X-ray luminosity, and source softness was observed. We also report X-ray emission from supernova 2008bk, refining its position, and suggest two candidate X-ray SNRs with soft, non-variable spectra, one resembling the identified X-ray SNRs
A Very Large Telescope imaging and spectroscopic survey of the Wolf-Rayet population in NGC 7793*
No full textWe present a Very Large Telescope/Focal Reducer and Low Dispersion Spectrograph #1 (VLT/FORS1) imaging and spectroscopic survey of the Wolf–Rayet (WR) population in the Sculptor group spiral galaxy NGC 7793. We identify 74 emission-line candidates from archival narrow-band imaging, from which 39 were observed with the Multi Object Spectroscopy mode of FORS1. 85 per cent of these sources displayed WR features. Additional slits were used to observe H ii regions, enabling an estimate of the metallicity gradient of NGC 7793 using strong line calibrations, from which a central oxygen content of log (O/H) + 12 = 8.6 was obtained, falling to 8.25 at R25. We have estimated WR populations using a calibration of line luminosities of Large Magellanic Cloud stars, revealing ∼27 WN and ∼25 WC stars from 29 sources spectroscopically observed. Photometric properties of the remaining candidates suggest an additional ∼27 WN and ∼8 WC stars. A comparison with the WR census of the LMC suggests that our imaging survey has identified ∼80 per cent of WN stars and ∼90 per cent for the WC subclass. Allowing for incompleteness, NGC 7793 hosts ∼105 WR stars for which N(WC)/N(WN) ∼ 0.5. From our spectroscopy of H ii regions in NGC 7793, we revise the global Hα star formation rate of Kennicutt et al. upward by 50 per cent to 0.45 M⊙ yr−1. This allows us to obtain N(WR)/N(O) ∼ 0.018, which is somewhat lower than that resulting from the WR census by Schild et al. of another Sculptor group spiral NGC 300, whose global physical properties are similar to NGC 7793. Finally, we also report the fortuitous detection of a bright (mV= 20.8 mag) background quasar Q2358-32 at z∼ 2.02 resulting from C ivλ1548-51 redshifted to the λ4684 passband
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Deep Fabry-Perot Halpha Observations of NGC 7793: a Very Extended Halpha Disk and a Truly Declining Rotation Curve
No full text28 pages, 8 figures. Accepted for publication in AJInternational audienceDeep Halpha observations of the Sculptor Group galaxy NGC 7793 were obtained on the ESO 3.60m and the Marseille 36cm telescopes at La Silla, Chile. Halpha emission is detected all the way to the edge of the HI disk, making of the HII disk of NGC 7793 one of the largest ever observed in a quiet non-AGN late-type system. Even in the very outer parts, the HII ionizing sources are probably mainly internal (massive stars in the disk) with an unlikely contribution from the extragalactic ionizing background. The Halpha kinematics confirms what had already been seen with the HI observations: NGC 7793 has a truly declining rotation curve. However, the decline is not Keplerian and a dark halo is still needed to explain the rotation velocities in the outer parts
- …
