The European Large Area ISO Survey - VI. Discovery of a new hyperluminous infrared galaxy

in Monthly Notices of the Royal Astronomical Society (2001), 327

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is ... [more ▼]

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is found to be a broad-line, radio-quiet quasar at a redshift [formmu4]z=1.099. From a detailed multicomponent model fit of the spectral energy distribution, we derive a total IR luminosity L[SUB]IR[/SUB] [formmu5](1-1000μm)~1.0à 10[SUP]13[/SUP]h65-2L[SUB]solar[/SUB] [formmu6](q[SUB]0[/SUB]=0.5), and discuss the possible existence of a starburst contributing to the far-IR output. Observations to date present no evidence for lens magnification. This galaxy is one of the very few HyLIGs with a X-ray detection. On the basis of its soft X-ray properties, we suggest that this broad-line object may be the face-on analogue of narrow-line, Seyfert-like HyLIGs. [less ▲]

Mid-FIR Properties of ELAIS Sources

in The Promise of the Herschel Space Observatory (2001, July 01)

We present the properties of all the galaxies detected by ISO at 7, 15 and 90 microns in ELAIS northern fields. The spectral energy distribution (SED) of those 20 galaxies with IRAS detections can ... [more ▼]

We present the properties of all the galaxies detected by ISO at 7, 15 and 90 microns in ELAIS northern fields. The spectral energy distribution (SED) of those 20 galaxies with IRAS detections can generally be well fitted by a predominant cirrus component plus a modest starburst contribution. Follow-up spectroscopy has shown that all the objects are emission-line galaxies but without a very intense star formation event. Most of the galaxies analyzed by means of optical R band photometry result to host an important exponential disk component, in good agreement with the SED IR modelling. We note that galaxies with morphological signs of perturbations seem to show slightly higher f[SUB]15[/SUB]/f[SUB]6.7[/SUB] ratios, indicating that star formation could be more important in them. One of the objects is a broad-line, radio-quiet quasar at z=1.099; its spectral energy distribution indicates that it is a hyperluminous infrared galaxy (HLIG), the first HLIG detected in the ELAIS areas. [less ▲]

The European Large Area ISO Survey - IV. The preliminary 90-microns luminosity function

in Monthly Notices of the Royal Astronomical Society (2001), 322

We present the luminosity function of 90-μm-selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities are in the range 10[SUP]9[/SUP]< h 65 -2L/L[SUB]solar ... [more ▼]

We present the luminosity function of 90-μm-selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities are in the range 10[SUP]9[/SUP]< h 65 -2L/L[SUB]solar[/SUB]<10[SUP]12[/SUP], i.e. non-ultraluminous. From our sample of 37 reliably detected galaxies in the ELAIS S1 region from the Efstathiou et al. S[SUB]90[/SUB]>=100mJy data base, we have found optical, 15-μm or 1.4-GHz identifications for 24 (65 per cent). We have obtained 2dF and UK Schmidt FLAIR spectroscopy of 89 per cent of identifications to rigid multivariate flux limits. We construct a luminosity function assuming that (i) our spectroscopic subset is an unbiased sparse sample, and (ii) there are no galaxies that would not be represented in our spectroscopic sample at any redshift. We argue that we can be confident of both assumptions. We find that the luminosity function is well described by the local 100-μm luminosity function of Rowan-Robinson, Helou & Walker. Assuming this local normalization, we derive luminosity evolution of (1+z)[SUP]2.45+/-0.85[/SUP] (95 per cent confidence). We argue that star formation dominates the bolometric luminosities of these galaxies, and we derive comoving star formation rates in broad agreement with the Flores et al. and Rowan-Robinson et al. mid-infrared-based estimates. [less ▲]

The European Large Area ISO Survey - I. Goals, definition and observations

in Monthly Notices of the Royal Astronomical Society (2000), 316

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT ... [more ▼]

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6deg[SUP]2[/SUP] being covered at 6.7μm and 1deg[SUP]2[/SUP] at 175μm. This paper discusses the goals of the project and the techniques employed in its construction, as well as presenting details of the observations carried out, the data from which are now in the public domain. We outline the ELAIS `preliminary analysis' which led to the detection of over 1000 sources from the 15 and 90-μm surveys (the majority selected at 15μm with a flux limit of ~3mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISOCAM and ISOPHOT. We detail how the ELAIS survey complements other ISO surveys in terms of depth and areal coverage, and show that the extensive multi-wavelength coverage of the ELAIS fields resulting from our concerted and on-going follow-up programme has made these regions amongst the best studied areas of their size in the entire sky, and, therefore, natural targets for future surveys. This paper accompanies the release of extremely reliable subsets of the `preliminary analysis' products. Subsequent papers in this series will give further details of our data reduction techniques, reliability and completeness estimates and present the 15- and 90-μm number counts from the `preliminary analysis', while a further series of papers will discuss in detail the results from the ELAIS `final analysis', as well as from the follow-up programme. [less ▲]

An investigation of the large-scale variability of the apparently single Wolf-Rayet star WR 1

in Astronomy and Astrophysics (1999), 349

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with ... [more ▼]

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with the existence of an unseen (collapsed?) companion or of spatially extended wind structures as potential candidates. We present observations of <ASTROBJ>WR 1</ASTROBJ> which highlight the unusual character of the variations in this object. Our narrowband photometric observations reveal a gradual increase of the stellar continuum flux amounting to Delta v ~ 0.09 mag followed by a decline on about the same timescale (3-4 days). Only marginal evidence for variability is found during the 11 following nights. Strong, daily line-profile variations are also observed but they cannot be easily linked to the photometric variations. Similarly to the continuum flux variations, coherent time-dependent changes are observed in 1996 in the centroid, equivalent width, and skewness of He Ii lambda 4686. Despite the generally coherent nature of the variations, we do not find evidence in our data for the periods claimed in previous studies. While the issue of a cyclical pattern of variability in <ASTROBJ>WR 1</ASTROBJ> is still controversial, it is clear that this object might constitute in the future a cornerstone for our understanding of the mechanisms leading to the formation of largely anisotropic outflows in Wolf-Rayet stars. [less ▲]

Sur la nature de la variabilite spectrale et photometrique periodique d'etoiles Wolf-Rayet apparemment isolees

Doctoral thesis (1999)

Il est depuis longtemps suspecté que les étoiles Wolf-Rayet apparemment isolées présentant des variations périodiques dans le profil de leurs raies spectrales, en photométrie ou en polarimétrie ... [more ▼]

Il est depuis longtemps suspecté que les étoiles Wolf-Rayet apparemment isolées présentant des variations périodiques dans le profil de leurs raies spectrales, en photométrie ou en polarimétrie sont associées à un compagnon dégénéré (étoile à neutron ou trou noir), et constituent ainsi une phase évolutive dont l'existence, bien que prédite par les modèles évolutifs des systèmes binaires massifs rapprochés, n'a pas encore été catégoriquement confirmée observationnellement. Cependant, de récentes études ayant trait à la variabilité spectrale des étoiles OB laissent émettre quelques doutes quant à la pertinence de ce modèle, en démontrant que des vents largement asphériques peuvent se développer dans les étoiles de type précoce. Le scénario alternatif serait donc de considérer que la variabilité périodique observée n'est pas due à la présence d'un compagnon dégénéré affectant la structure à grande échelle du vent de l'étoile Wolf-Rayet, mais est au contraire induite par la modulation par rotation d'un vent nettement anisotropique. Cet ouvrage présente les résultats d'un vaste programme d'observations spectroscopiques et photométriques (généralement simultanées) se proposant de lever l'ambiguïté sur la nature précise des étoiles Wolf-Rayet apparemment isolées dont la périodicité des variations est. soit depuis longtemps établie (WR 6), soit suspectée (WR 1, WR 134, WR 136). Notre étude a permis de confirmer l'existence d'une périodicité de 2.3 jours pour l'étoile WR 134. En outre, nous présentons des arguments mettant en doute l'éventuelle association de WR 6 et WR 134 avec un compagnon dégénéré. Alternativement, nous proposons que la variabilité périodique observée serait plutôt induite, à l'instar de nombreuses étoiles OB, par la rotation de structures azimutalement étendues dans le vent. Ce modèle est plus à même d'appréhender certains aspects de la variabilité, notamment la nature globalement différente du patron de variabilité selon l'époque d'observation, le caractère périodique des variations présentées par les raies spectrales formées à proximité du coeur stellaire, ou encore la causalité des variations affectant les parties internes et externesdu vent. Cette assertion est également supportée par la déficience de rayons-X observée dans le contexte d'une accrétion du vent stellaire par un objet dégénéré. La similitude des variations spectrales de l'étoile WR 1 avec celles des étoiles précitées laisse présumer qu'une variabilité de nature cyclique pourrait éventuellement être révélée dans un proche avenir. Dans ce cas de figure, nos données semblent imposer une limite inférieure de 5 jours pour une quelconque périodicité. Le cas échéant, ces structures à grande échelle dans le vent des étoiles WR 6 et WR 134 doivent probablement leur formation à une activité photosphérique dont la nature précise reste à déterminer. L'existence de pulsations radiales ou non radiales du noyau, ou de structures magnétiques (``photosphériques'' ou plus vraisemblablement d'origine fossile) pourrait néanmoins être à l'origine de ce phénomène. [less ▲]

Variabilite cyclique d'etoiles Wolf-Rayet apparemment isolees.

in Journal of the Royal Astronomical Society of Canada (1998), 92

Not Available

Coupled Line-Profile and Continuum Variations in EZ Canis Majoris: Implications for the Driving Mechanism of Global Wind Structures in Wolf-Rayet Winds

in Astrophysical Journal (1998), 498

EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequence that exhibits strong variations on a period of 3.77 days with coherency lasting typically about 10 cycles. We have used an ... [more ▼]

EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequence that exhibits strong variations on a period of 3.77 days with coherency lasting typically about 10 cycles. We have used an extensive set of optical spectroscopic observations to investigate a possible link between its line-profile and photometric continuum variability. Despite the strong epoch dependency of the variations, a persistent correlation is found between changes in the wind line profiles (N V lambda lambda 4604, 4620 in particular) and in continuum flux emanating near the stellar core. We suggest that these observations give further support to the idea that the physical conditions prevailing in the vicinity of the star's photosphere have a significant impact on the wind structure and that a spatial dependence of these conditions at the base of the outflow induces the formation of azimuthal wind structures in EZ CMa. The epoch-dependent nature of the variability could be related to long-term behavior of corotating magnetic structures, although pulsational instabilities constitute a viable alternative. [less ▲]

Confirmation of a 2.3-DAY Periodicity in the Wolf-Rayet Star WR 134: a Twin of EZ Cma?

in Cyclical Variability in Stellar Winds (1998)

Not Available

Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind

in Astrophysical Journal (1997), 482

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also ... [more ▼]

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also monitored EZ CMa using narrowband photometry. The light curve was found to be remarkably stable when folded with the P=3.77 day period, and it had a peak-to-valley amplitude of 0.1 mag. The P Cygni absorption components of He I lambda 3889 and He I lambda 5876 display a similar global pattern of variability as was found for the simultaneously acquired UV profiles. The strengthening of the P Cygni absorption component of these transitions is associated with the maximum of the continuum flux. Conversely, the absorption trough of N V lambda 4604 gradually disappears as the star brightens. Although the emission parts of the lines are variable at different levels, they all show the same pattern of variability, which consists of phase-dependent shifts of extra emission components superposed on the profiles. A strong correlation is found between the continuum-light level and the equivalent width of most transitions. The line skewness and the full-width at half-maximum show a daily recurrence timescale, reflecting the light curve changes. We have addressed in a rigorous statistical way the significance of the variations by calculating the "temporal variance spectrum." For any given line, we found enhanced variability at some velocities, although the whole profile displays a statistically significant level of variability. Arguments against a compact companion as the cause of the observed periodic variability are presented. Instead, our observations strongly support the suggestion in the IUE Mega analysis that the atypical level of variability results from the rotation of a structured wind. We propose that the wind variability of EZ CMa is triggered by photospheric activity, or that the wind is controlled by a large-scale magnetic field. [less ▲]