Context. The Vela Molecular Ridge is one of the nearest (700 pc) giant molecular cloud (GMC) complexes hosting intermediate-mass (up to early B, late O stars) star formation, and is located in the ...outer Galaxy, inside the Galactic plane. Vela C is one of the GMCs making up the Vela Molecular Ridge, and exhibits both sub-regions of robust and sub-regions of more quiescent star formation activity, with both low- and intermediate(high)-mass star formation in progress. Aims. We aim to study the individual and global properties of dense dust cores in Vela C, and aim to search for spatial variations in these properties which could be related to different environmental properties and/or evolutionary stages in the various sub-regions of Vela C. Methods. We mapped the submillimetre (345 GHz) emission from vela C with LABOCA (beam size ~19′′2, spatial resolution ~0.07 pc at 700 pc) at the APEX telescope. We used the clump-finding algorithm CuTEx to identify the compact submillimetre sources. We also used SIMBA (250 GHz) observations, and Herschel and WISE ancillary data. The association with WISE red sources allowed the protostellar and starless cores to be separated, whereas the Herschel dataset allowed the dust temperature to be derived for a fraction of cores. The protostellar and starless core mass functions (CMFs) were constructed following two different approaches, achieving a mass completeness limit of 3.7 M⊙. Results. We retrieved 549 submillimetre cores, 316 of which are starless and mostly gravitationally bound (therefore prestellar in nature). Both the protostellar and the starless CMFs are consistent with the shape of a Salpeter initial mass function in the high-mass part of the distribution. Clustering of cores at scales of 1–6 pc is also found, hinting at fractionation of magnetised, turbulent gas.
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A quasar microlensing event towards J1249+3449? De Paolis, F; Nucita, A A; Strafella, F ...
Monthly notices of the Royal Astronomical Society. Letters,
11/2020, Volume:
499, Issue:
1
Journal Article
Peer reviewed
ABSTRACT
We show that the optical flare event discovered by Graham et al. towards the active galactic nucleus J1249+3449 is fully consistent with being a quasar microlensing event due to a ≃0.1 M⊙ ...star, although other explanations, such as that, mainly supported by Graham et al., of being the electromagnetic counterpart associated with a binary black hole merger, cannot be completely excluded at present.
ABSTRACT
We report on the XMM–Newton observation of HP Cet and Swift J0820.6–2805, two X-ray photon sources that are candidates to be members of the intermediate polar class of cataclysmic variables. ...If the historical optical light curve of HP Cet shows a periodic feature at ≃96 min, a clear identification of such a signature in the high energy band (apart for a variability on a time-scale of ≃8 min as detected by the ROSAT satellite) is lacking. By using XMM–Newton archive data, we clearly identify a feature (at ≃88 min) which is marginally consistent with one of the binary system orbital periods reported in the literature. We also found a signature of a periodic features on the time-scale of ≃5.6 min. In the case of Swift J0820.6–2805, the intermediate polar nature was previously unclear and the orbital and the white dwarf spin periods were unknown. Here, the 0.3–10 keV data undoubtedly reveal an orbital period and a white dwarf spin of ≃87.5 and ≃27.9 min, respectively. The spectral analysis showed that both HP Cet and Swift J0820.6–280 are members of the underluminous IP subclass since their luminosity in the 0.3–10 keV band is estimated to be ≃5 × 1030 and ≃3.8 × 1029 erg s−1, respectively.
ABSTRACT
We present the 360° catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 $\mu$m. This release not only completes the analogous catalogue previously ...produced by the Hi-GAL collaboration for −71° ≲ ℓ ≲ 67°, but also meaningfully improves it because of a new set of heliocentric distances, 120 808 in total. About a third of the 150 223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 $\mu$m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23 per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from λ = 21 to 1100 $\mu$m, gives the source luminosity and other bolometric quantities, while a modified blackbody fitted to data for $\lambda \ge 160~\mu$m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions.
Abstract
The transient event labelled as TCP J05074264+2447555 recently discovered towards the Taurus region was quickly recognized to be an ongoing microlensing event on a source located at distance ...of only 700–800 pc from Earth. Here, we show that observations with high sampling rate close to the time of maximum magnification revealed features that imply the presence of a binary lens system with very low-mass ratio components. We present a complete description of the binary lens system, which host an Earth-like planet with most likely mass of 9.2 ± 6.6 M⊕. Furthermore, the source estimated location and detailed Monte Carlo simulations allowed us to classify the event as due to the closest lens system, being at a distance of ≃380 pc and mass ≃0.25 M⊙.
ABSTRACT
Intermediate polars are a class of cataclysmic variables in which a white dwarf accretes material from a companion star. The intermediate polar nature confirmation usually derives from the ...detection of two periods in both X-ray and optical photometry. In this respect, the high-energy signal is often characterized by modulations on the white dwarf spin and the orbital period. However, noting that the periodograms may be characterized by strong features also at the synodic period and/or other sidebands, the timing analysis of the X-ray signal may offer the unique possibility to firmly discover an intermediate polar candidate. Here, we concentrate on a sample of five cataclysmic variable binary candidates: i.e. SAXJ1748.2-2808, 1RXS J211336.1 + 542226, CXOGC J174622.7-285218, CXOGC J174517.4-290650, and V381 Vel, listed in the IPHome catalogue. Our main aim is to confirm if they belong to the intermediate polar class or not. The results of our analysis show that we can safely assess the intermediate polar nature of all the considered sources, apart for the case of V381 Vel which instead behaves like a cataclysmic variable of the polar subclass. Moreover, the source SAXJ1748.2-2808, previously classified as an HMXB, appears to be, most likely, an intermediate polar variable.
Intermediate polars are members of the cataclysmic variable binary stars. They are characterized by a moderately magnetized white dwarf accreting matter from a cool main-sequence companion star. In ...many cases, this accretion gives rise to a detectable X-ray emission. VZ Sex is an interesting X-ray source whose nature needs a robust confirmation. Here, we used archived XMM-Newton observations to assign the source to the intermediate polar class. We applied the Lomb-Scargle periodogram method to detect any relevant periodic feature in the 0.1-10 keV light curve and performed a spectral fitting of the X-ray spectrum in order to get information on the on-going accretion mechanism. By inspecting the periodogram, we detected a clear periodic feature at 20.3 minutes that we interpret as the spin period of the white dwarf. We additionally found the typical side bands expected as the consequence of the beat between the spin and the orbital period of 3.581 hr. The source is characterized by an unabsorbed flux of 2.98 × 10−12 erg cm−2 s−1 corresponding to an intrinsic luminosity of 7 × 1031 erg s−1 for a distance of 433 pc. The existence of such features allows us to classify VZ Sex as a clear member of the intermediate polar class. Furthermore, with the estimated WD spin, the ratio Pspin/Porb is 0.09, i.e., consistent with that expected for a typical IP system above the period gap. In addition, the estimated intrinsic luminosity opens the possibility that a bridge linking the normally bright IPs to the faint population of sources does exist.
Context.
V1118 Ori is a classical EXor source whose light curve has been monitored, although not continuously, over the past 30 years. This source underwent a powerful outburst in 2005, followed by ...10 years of quiescence and a less intense outburst in 2015. In 2019, a new intense brightness increase was observed (Δ
g
∼ 3 mag).
Aims.
This new accretion episode offers the opportunity to compare the photometric and spectroscopic properties of multiple outbursts of the same source. This allows us to highlight the differences and similarities among various events by removing any possible bias related to the intrinsic properties of the star-disk system.
Methods.
We discovered the 2019 V1118 Ori outburst by examining the
g
-band light curve acquired by the Zwicky Transient Facility and followed the declining phase with the Rapid Eye Mount telescope in the
griz
bands. Two near-infrared spectra were also acquired at different brightness stages with the Large Binocular Telescope.
Results.
The last event shows the following characteristics: (1) an amplitude similar to that of 2015 and lower than that of 2005; (2) a duration of less than one year as in previous events; (3) a increasing (decreasing) speed of 0.018 (0.031) mag day
−1
, which is different from previous cases; (4) a gradually blueing of the
g
−
r
color is observed over time, while the
r
−
i
color remains roughly unchanged; (5) with few exceptions, the near-infrared lines (mainly H
I
recombination) are the same as those observed in 2015; and (6) the mass accretion rate peaks at
Ṁ
acc
∼ 10
−7
M
⊙
yr
−1
and decreases in about a month down to a few 10
−8
M
⊙
yr
−1
.
Conclusions.
Our analysis shows that the comparison of data from different outbursts of the same source is a nontrivial exercise, which allows us to obtain important clues that are useful to drive theoretical efforts toward a better understanding of the EXor phenomenon.
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We report far-infrared Herschel observations obtained between 70 μm and 500 μm of two star-forming dusty condensations, HKM99 B1-bS and HKM99 B1-bN, in the B1 region of the Perseus star-forming ...cloud. In the western part of the Perseus cloud, B1-bS is the only source detected in all six PACS and SPIRE photometric bands, but it is not visible in the Spitzer map at 24 μm. B1-bN is clearly detected between 100 μm and 250 μm. We have fitted the spectral energy distributions of these sources to derive their physical properties, and find that a simple greybody model fails to reproduce the observed spectral energy distributions. At least a two-component model is required, consisting of a central source surrounded by a dusty envelope. The properties derived from the fit, however, suggest that the central source is not a Class 0 object. We then conclude that while B1-bS and B1-bN appear to be more evolved than a pre-stellar core, the best-fit models suggest that their central objects are younger than a Class 0 source. Hence, they may be good candidates to be examples of the first hydrostatic core phase. The projected distance between B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close to this value, this pair would allow studying the mutual interactions between two forming stars at a very early stage of their evolution.
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After a quiescence period of about 10 years, the classical EXor source V1118 Ori has undergone an accretion outburst in 2015 September. The maximum brightness ( mag) was reached in 2015 December and ...was maintained for several months. Since 2016 September, the source is in a declining phase. Photometry and low/high-resolution spectroscopy were obtained with MODS and LUCI2 at the Large Binocular Telescope, with the facilities at the Asiago 1.22 and 1.82 m telescopes, and with GIANO at the Telescopio Nazionale Galileo. The spectra are dominated by emission lines of H i and neutral metallic species. From line and continuum analysis we derive the mass accretion rate and its evolution during the outburst. Considering that extinction may vary between 1.5 and 2.9 mag, we obtain = 0.3-2.0 10−8 M yr−1 in quiescence and = 0.2-1.9 10−6 M yr−1 at the outburst peak. The Balmer decrement shape has been interpreted by means of line excitation models, finding that from quiescence to outburst peak, the electron density has increased from ∼2 109 cm−3 to ∼4 1011 cm−3. The profiles of the metallic lines are symmetric and narrower than 100 km s−1, while H i and He i lines show prominent wings extending up to 500 km s−1. The metallic lines likely originate at the base of the accretion columns, where neutrals are efficiently shielded against the ionizing photons, while faster ionized gas is closer to the star. Outflowing activity is testified by the detection of a variable P Cyg-like profile of the H and He i 1.08 m lines.
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