DW Cancri in X-rays Nucita, A A; Conversi, L; Licchelli, D
Monthly notices of the Royal Astronomical Society,
04/2019, Letnik:
484, Številka:
3
Journal Article
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ABSTRACT
We report on the XMM–Newton observation of DW Cnc, a candidate intermediate polar candidate whose historical optical light curve shows the existence of periods at ≃38, ≃86, and ≃69 min, ...which were interpreted as the white dwarf spin, the orbital and the spin–orbit beat periodicities. By studying the 0.3–10 keV light curves, we confirm the existence of a period at ≃ 38 min and find in the OM light curve a signature for a period at 75 ± 21 min, which is consistent with both the orbital and spin–orbit beat. These findings allow us to unveil without any doubt, the nature of DW Cnc as an accreting intermediate polar. The EPIC and RGS source spectra were analysed and a best-fitting model, consisting of a multitemperature plasma, was found. The maximum temperature found when fitting the data is kTmax ≃ 31 keV, which can be interpreted as an upper limit to the temperature of the shock.
We describe the procedure used to flux calibrate the three-band submillimetre photometer in the Spectral and Photometric Imaging Receiver instrument on the Herschel Space Observatory. This includes ...the equations describing the calibration scheme, a justification for using Neptune as the primary calibration source, a description of the observations and data processing procedures used to derive flux calibration parameters (for converting from voltage to flux density) for every bolometer in each array, an analysis of the error budget in the flux calibration for the individual bolometers and tests of the flux calibration on observations of primary and secondary calibrators. The procedure for deriving the flux calibration parameters is divided into two parts. In the first part, we use observations of astronomical sources in conjunction with the operation of the photometer internal calibration source to derive the unscaled derivatives of the flux calibration curves. To scale the calibration curves in Jy beam−1 V−1, we then use observations of Neptune in which the beam of each bolometer is mapped using a very fine scan pattern. The total instrumental uncertainties in the flux calibration for most individual bolometers is ∼0.5 per cent, although a few bolometers have uncertainties of ∼1-5 per cent because of issues with the Neptune observations. Based on application of the flux calibration parameters to Neptune observations performed using typical scan map observing modes, we determined that measurements from each array as a whole have instrumental uncertainties of 1.5 per cent. This is considerably less than the absolute calibration uncertainty associated with the model of Neptune, which is estimated at 4 per cent.
ABSTRACT
We present SCUBA-2 850 $\mathrm{ \mu}$m observations of 13 candidate starbursting protoclusters selected using Planck and Herschel data. The cumulative number counts of the 850 $\mathrm{ ...\mu}$m sources in 9 of 13 of these candidate protoclusters show significant overdensities compared to the field, with the probability <10−2 assuming the sources are randomly distributed in the sky. Using the 250, 350, 500, and 850 $\mathrm{ \mu}$m flux densities, we estimate the photometric redshifts of individual SCUBA-2 sources by fitting spectral energy distribution templates with an MCMC method. The photometric redshift distribution, peaking at 2 < z < 3, is consistent with that of known z > 2 protoclusters and the peak of the cosmic star formation rate density (SFRD). We find that the 850 $\mathrm{ \mu}$m sources in our candidate protoclusters have infrared luminosities of $L_{\mathrm{IR}}\gtrsim 10^{12}\, \mathrm{L}_{\odot }$ and star formation rates of SFR = (500–1500) M⊙ yr−1. By comparing with results in the literature considering only Herschel photometry, we conclude that our 13 candidate protoclusters can be categorized into four groups: six of them being high-redshift starbursting protoclusters, one being a lower redshift cluster or protocluster, three being protoclusters that contain lensed dusty star-forming galaxies or are rich in 850 $\mathrm{ \mu}$m sources, and three regions without significant Herschel or SCUBA-2 source overdensities. The total SFRs of the candidate protoclusters are found to be comparable or higher than those of known protoclusters, suggesting our sample contains some of the most extreme protocluster population. We infer that cross-matching Planck and Herschel data is a robust method for selecting candidate protoclusters with overdensities of 850 $\mathrm{ \mu}$m sources.
Abstract
Trojan asteroids are small bodies orbiting around the
L
4
or
L
5
Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System ...evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK
7
has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL
5
is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL
5
will remain in
L
4
for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be
$${H}_{r}=18.5{8}_{-0.15}^{+0.16}$$
H
r
=
18.5
8
−
0.15
+
0.16
, and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid.
Photometric instruments operating at far-infrared to millimetre wavelengths often have broad spectral passbands (λ/Δλ ∼ 3 or less), especially those operating in space. A broad passband can result in ...significant variation of the beam profile and aperture efficiency across the passband, effects which thus far have not generally been taken into account in the flux calibration of such instruments. With absolute calibration uncertainties associated with the brightness of primary calibration standards now in the region of 5 per cent or less, variation of the beam properties across the passband can be a significant contributor to the overall calibration accuracy for extended emission. We present a calibration framework which takes such variations into account for both antenna-coupled and absorber-coupled focal plane architectures. The scheme covers point source and extended source cases, and also the intermediate case of a semi-extended source profile. We apply the new method to the Spectral and Photometric Imaging Receiver (SPIRE) photometer on board the Herschel Space Observatory.
Context.
Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, ...previously ignored systematic effects must be addressed.
Aims.
In this work, we evaluate the impact of the reduced shear approximation and magnification bias on information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities in high-magnification regions.
Methods.
The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculated the impact of neglecting these effects on the cosmological parameters that would be determined from
Euclid
, using cosmic shear tomography. To do so, we employed the Fisher matrix formalism, and included the impact of the super-sample covariance. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach.
Results.
These effects cause significant biases in Ω
m
,
σ
8
,
n
s
, Ω
DE
,
w
0
, and
w
a
of −0.53
σ
, 0.43
σ
, −0.34
σ
, 1.36
σ
, −0.68
σ
, and 1.21
σ
, respectively. We then show that these lensing biases interact with another systematic effect: the intrinsic alignment of galaxies. Accordingly, we have developed the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to
Euclid
, we find that the additional terms introduced by this correction are sub-dominant.
HerMES: The SPIRE confusion limit Nguyen, H. T.; Schulz, B.; Levenson, L. ...
Astronomy and astrophysics (Berlin),
07/2010, Letnik:
518, Številka:
1
Journal Article
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We report on the sensitivity of SPIRE photometers on the Herschel Space Observatory. Specifically, we measure the confusion noise from observations taken during the science demonstration phase of the ...Herschel Multi-tiered Extragalactic Survey. Confusion noise is defined to be the spatial variation of the sky intensity in the limit of infinite integration time, and is found to be consistent among the different fields in our survey at the level of 5.8, 6.3 and 6.8 mJy/beam at 250, 350 and 500 μm, respectively. These results, together with the measured instrument noise, may be used to estimate the integration time required for confusion limited maps, and provide a noise estimate for maps obtained by SPIRE.
Context. CMB experiments aiming at a precise measurement of the CMB polarization, such as the Planck satellite, need a strong polarized absolute calibrator on the sky to accurately set the detectors ...polarization angle and the cross-polarization leakage. As the most intense polarized source in the microwave sky at angular scales of few arcminutes, the Crab nebula will be used for this purpose. Aims. Our goal was to measure the Crab nebula polarization characteristics at 90 GHz with unprecedented precision. Methods. The observations were carried out with the IRAM 30 m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers. Results. We processed the Stokes I, Q, and U maps from our observations in order to compute the polarization angle and linear polarization fraction. The first is almost constant in the region of maximum emission in polarization with a mean value of αSky = 152.1±0.3° in equatorial coordinates, and the second is found to reach a maximum of Π = 30% for the most polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam will see a mean polarization angle of αSky = 149.9±0.2° and a mean polarization fraction of Π = 8.8±0.2%.
Weak lensing, which is the deflection of light by matter along the line of sight, has proven to be an efficient method for constraining models of structure formation and reveal the nature of dark ...energy. So far, most weak-lensing studies have focused on the shear field that can be measured directly from the ellipticity of background galaxies. However, within the context of forthcoming full-sky weak-lensing surveys such as
Euclid
, convergence maps (mass maps) offer an important advantage over shear fields in terms of cosmological exploitation. While it carry the same information, the lensing signal is more compressed in the convergence maps than in the shear field. This simplifies otherwise computationally expensive analyses, for instance, non-Gaussianity studies. However, the inversion of the non-local shear field requires accurate control of systematic effects caused by holes in the data field, field borders, shape noise, and the fact that the shear is not a direct observable (reduced shear). We present the two mass-inversion methods that are included in the official
Euclid
data-processing pipeline: the standard Kaiser & Squires method (KS), and a new mass-inversion method (KS+) that aims to reduce the information loss during the mass inversion. This new method is based on the KS method and includes corrections for mass-mapping systematic effects. The results of the KS+ method are compared to the original implementation of the KS method in its simplest form, using the
Euclid
Flagship mock galaxy catalogue. In particular, we estimate the quality of the reconstruction by comparing the two-point correlation functions and third- and fourth-order moments obtained from shear and convergence maps, and we analyse each systematic effect independently and simultaneously. We show that the KS+ method substantially reduces the errors on the two-point correlation function and moments compared to the KS method. In particular, we show that the errors introduced by the mass inversion on the two-point correlation of the convergence maps are reduced by a factor of about 5, while the errors on the third- and fourth-order moments are reduced by factors of about 2 and 10, respectively.
We compare the absolute gain photometric calibration of the Planck/HFI and Herschel/SPIRE instruments on diffuse emission. The absolute calibration of HFI and SPIRE each relies on planet flux ...measurements and comparison with theoretical far-infrared emission models of planetary atmospheres. We measure the photometric cross calibration between the instruments at two overlapping bands, 545GHz/500 mu m and 857GHz/350 mu m. The HFI maps are bandpass-corrected to match the emission observed by the SPIRE bandpasses. The SPIRE maps are convolved to match the HFI beam and put on a common pixel grid. We measure the cross-calibration relative gain between the instruments using two methods in each field, pixel-to-pixel correlation and angular power spectrum measurements. Of the 5.5% uncertainty for SPIRE, 4% arises from the uncertainty of the effective beam solid angle, which impacts the adopted SPIRE point source to extended source unit conversion factor, highlighting that as a focus for refinement.
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