We present the results of three-year monitoring campaigns of the z = 0.024 type 1 active Galactic nucleus (AGN) PGC 50427. Using robotic telescopes of the Universitätssternwarte Bochum near Cerro ...Armazones in Chile, we monitored PGC 50427 in the optical and near-infrared (NIR). Through the use of photometric reverberation mapping with broad- and narrowband filters, we determine the size of the broad-line emitting region by measuring the time delay between the variability of the continuum and the Hα emission line. The Hα emission line responds to blue continuum variations with an average rest frame lag of 19.0 ± 1.23 days. Using single epoch spectroscopy obtained with the Southern African Large Telescope (SALT) we determined a broad-line Hα velocity width of 1020 km s-1 and in combination with the rest frame lag and adoption of a geometric scaling factor f = 5.5, we calculate a black hole mass of MBH ~ 17 × 106 M⊙. Using the flux variation gradient method, we separate the host galaxy contribution from that of the AGN to calculate the rest frame 5100 Å luminosity at the time of our monitoring campaign. We measured small luminosity variations in the AGN (~10%) accross the three years of the monitoring campaign. The rest frame lag and the host-subtracted luminosity permit us to derive the position of PGC 50427 in the BLR size – AGN luminosity diagram, which is remarkably close to the theoretically expected relation of R ∝ L0.5. The simultaneous optical and NIR (J and Ks) observations allow us to determine the size of the dust torus through the use of dust reverberation mapping method. We find that the hot dust emission (~1800 K) lags the optical variations with an average rest frame lag of 46.2 ± 2.60 days. The dust reverberation radius and the nuclear NIR luminosity permit us to derive the position of PGC 50427 on the known τ − MV diagram. The simultaneous observations for the broad-line region and dust thermal emission demonstrate that the innermost dust torus is located outside the BLR in PGC 50427, supporting the unified scheme for AGNs.
The variability of young stellar objects (YSO) changes their brightness and color preventing a proper classification in traditional color−color and color magnitude diagrams. We have explored the ...feasibility of the flux variation gradient (FVG) method for YSOs, using H and K band monitoring data of the star forming region RCW 38 obtained at the University Observatory Bochum in Chile. Simultaneous multi-epoch flux measurements follow a linear relation FH = α + β·FK for almost all YSOs with large variability amplitude. The slope β gives the mean HK color temperature Tvar of the varying component. Because Tvar is hotter than the dust sublimation temperature, we have tentatively assigned it to stellar variations. If the gradient does not meet the origin of the flux-flux diagram, an additional non- or less-varying component may be required. If the variability amplitude is larger at the shorter wavelength, e.g. α< 0, this component is cooler than the star (e.g. a circumstellar disk); vice versa, if α> 0, the component is hotter like a scattering halo or even a companion star. We here present examples of two YSOs, where the HK FVG implies the presence of a circumstellar disk; this finding is consistent with additional data at J and L. One YSO shows a clear K-band excess in the JHK color−color diagram, while the significance of a K-excess in the other YSO depends on the measurement epoch. Disentangling the contributions of star and disk it turns out that the two YSOs have huge variability amplitudes (~3−5 mag). The HK FVG analysis is a powerful complementary tool to analyze the varying components of YSOs and worth further exploration of monitoring data at other wavelengths.
Context. Jets from young stars can be highly asymmetric and have multiple velocity components. Aims. To clarify the origin of jet asymmetries and constrain the launch mechanism, we study as a test ...case the physical and kinematical structure of the prototypical asymmetric flow emitted by DG Tau B. Methods. The analysis of deep, high spectral resolution observations taken with the KECK telescope allows us to infer the properties and the spatial distribution of the velocity components in the two jet lobes. From selected line ratios we derive the gas physical conditions (the electron and total density, ne and nH, the ionisation fraction, xe, and the temperature, Te), as a function of the distance from the source and the gas velocity. The presence of dust grains in the jet is investigated by estimating the gas-phase abundance of calcium with respect to its solar value. Results. The detected lines show broad velocity profiles at the base of the jet (up to ~100 km s-1), where up to three velocity components are detected. At 5′′from the source, however, only the denser and more excited high-velocity components survive and the lines are narrower (~10–30 km s-1). The jet is strongly asymmetric in the velocity and in its physical structure. The red lobe, which is slower (~140 km s-1) and more collimated (opening angle: α ~ 3–4°), presents low ionisation fractions (xe ~ 0.1–0.4) and temperatures (Te < 5 × 103 K), while the total density is up to ~2.5 × 104 cm-3. The blue lobe, faster (~–320 km s-1) and less collimated (α ~ 14°), is also less dense (nH < 104 cm-3), but highly excited (Te up to ~5 × 104 K and xe up to 0.9). The estimated mass-loss rate turns out to be similar in the two lobes (~6–8 × 10-9 M⊙ yr-1), while the flux of the linear momentum is three times higher in the blue one (~2.5 × 10-7 M⊙ yr-1 km s-1). Calcium is strongly depleted with respect to its solar abundance, indicating that the jet contains dust grains. The depletion is lower for higher velocities, which is consistent with dust destruction by shocks. Conclusions. The similar mass-loss rate in the two lobes suggests that the ejection power is comparable on the two sides of the system, as expected from a magneto-centrifugal ejection mechanism, and that the observed asymmetries are caused by a different mass load and propagation properties in an inhomogeneous environment. The presence of dust grains implies that the jet is generated from a region of the disc extending beyond the dust sublimation radius.
The binary system RW Aur consists of two classical T Tauri stars (CTTSs). The primary recently underwent its second observed major dimming event (ΔV ~ 2 mag). We present new, resolved Chandra X-ray ...and UKIRT near-IR (NIR) data as well as unresolved optical photometry obtained in the dim state to study the gas and dust content of the absorber causing the dimming. The X-ray data show that the absorbing column density increased from NH< 0.1 × 1022cm-2 during the bright state to ≈2 × 1022cm-2 in the dim state. The brightness ratio between dim and bright state at optical to NIR wavelengths shows only a moderate wavelength dependence and the NIR color–color diagram suggests no substantial reddening. Taken together, this indicates gray absorption by large grains (≳1 μm) with a dust mass column density of ≳2 × 10-4 g cm-2. Comparison with NH shows that an absorber responsible for the optical/NIR dimming and the X-ray absorption is compatible with the ISM’s gas-to-dust ratio, i.e., that grains grow in the disk surface layers without largely altering the gas-to-dust ratio. Lastly, we discuss a scenario in which a common mechanism can explain the long-lasting dimming in RW Aur and recently in AA Tau.
We present a search for eclipses of ~1700 white dwarfs (WDs) in the Pan-STARRS1 medium-deep fields. Candidate eclipse events are selected by identifying low outliers in over 4.3 million light curve ...measurements. We find no short-duration eclipses consistent with being caused by a planetary size companion. This large data set enables us to place strong constraints on the close-in planet occurrence rates around WDs for planets as small as 2 R sub(+ in circle). Our results indicate that gas giant planets orbiting just outside the Roche limit are rare, occurring around less than 0.5% of WDs. Habitable-zone super-Earths and hot super-Earths are less abundant than similar classes of planets around main-sequence stars. These constraints provide important insight into the ultimate fate of the large population of exoplanets orbiting main-sequence stars.
The Pan-Planets survey observed an area of 42 sq deg. in the galactic disk for about 165 h. The main scientific goal of the project is the detection of transiting planets around M dwarfs. We ...establish an efficient procedure for determining the stellar parameters Teff and log g of all sources using a method based on SED fitting, utilizing a three-dimensional dust map and proper motion information. In this way we identify more than 60 000 M dwarfs, which is by far the largest sample of low-mass stars observed in a transit survey to date. We present several planet candidates around M dwarfs and hotter stars that are currently being followed up. Using Monte Carlo simulations we calculate the detection efficiency of the Pan-Planets survey for different stellar and planetary populations. We expect to find 3.0+3.3-1.6 hot Jupiters around F, G, and K dwarfs with periods lower than 10 days based on the planet occurrence rates derived in previous surveys. For M dwarfs, the percentage of stars with a hot Jupiter is under debate. Theoretical models expect a lower occurrence rate than for larger main sequence stars. However, radial velocity surveys find upper limits of about 1% due to their small sample, while the Kepler survey finds a occurrence rate that we estimate to be at least 0.17b(+0.67-0.04) %, making it even higher than the determined fraction from OGLE-III for F, G and K stellar types, 0.14 (+0.15-0.076) %. With the large sample size of Pan-Planets, we are able to determine an occurrence rate of 0.11 (+0.37-0.02) % in case one of our candidates turns out to be a real detection. If, however, none of our candidates turn out to be true planets, we are able to put an upper limit of 0.34% with a 95% confidence on the hot Jupiter occurrence rate of M dwarfs. This limit is a significant improvement over previous estimates where the lowest limit published so far is 1.1% found in the WFCAM Transit Survey. Therefore we cannot yet confirm the theoretical prediction of a lower occurrence rate for cool stars.
ABSTRACT
We report the discovery of a resolved (0.9 arcsec) substellar companion to a member of the 1–5 Myr Taurus star-forming region. The host star (2M0437) is a single mid-M type (Teff ≈ 3100 K) ...dwarf with a position, space motion, and colour–magnitude that support Taurus membership, and possible affiliation with a ∼2.5-Myr-old subgroup. A comparison with stellar models suggests a 2–5 Myr age and a mass of 0.15–0.18M⊙. Although K2 detected quasi-periodic dimming from close-in circumstellar dust, the star lacks detectable excess infrared emission from a circumstellar disc and its H α emission is not commensurate with accretion. Astrometry based on 3 yr of AO imaging shows that the companion (2M0437b) is comoving, while photometry of two other sources at larger separation indicates that they are likely heavily reddened background stars. A comparison of the luminosity of 2M0437b with models suggests a mass of 3–5 MJUP, well below the deuterium burning limit, and an effective temperature of 1400–1500 K, characteristic of a late L spectral type. The H − K colour is redder than the typical L dwarf, but comparable to other directly detected young planets, e.g. those around HR 8799. The discovery of a super-Jupiter around a very young, very low-mass star challenges models of planet formation by either core accretion (which requires time) or disc instability (which requires mass). We also detected a second, comoving, widely separated (75 arcsec) object that appears to be a heavily extincted star. This is certainly a fellow member of this Taurus subgroup and statistically likely to be a bound companion.
We present the results of a pilot study for the extended Massive Cluster Survey (eMACS), a comprehensive search for distant, X-ray luminous galaxy clusters at z > 0.5. Our pilot study applies the ...eMACS concept to the 71 deg2 area extended by the 10 fields of the Pan-STARRS1 (PS1) Medium Deep Survey (MDS). Candidate clusters are identified by visual inspection of PS1 images in the g, r, i and z bands in a 5 × 5 arcmin2 region around X-ray sources detected in the ROSAT All-Sky Survey (RASS). To test and optimize the eMACS X-ray selection criteria, our pilot study uses the largest possible RASS data base, i.e. all RASS sources listed in the Bright and Faint Source Catalogues (BSC and FSC) that fall within the MDS footprint. We apply no additional constraints regarding X-ray flux, spectral hardness ratio or photon statistics and lower the redshift threshold to z > 0.3 to extend the probed luminosity range to poorer systems. Scrutiny of PS1/MDS images for 41 BSC and 200 FSC sources combined with dedicated spectroscopic follow-up observations results in a sample of 11 clusters with estimated or spectroscopic redshifts of z > 0.3. In order to assess and quantify the degree of point source contamination of the observed RASS fluxes, we examine archival Chandra data obtained in targeted and serendipitous observations of six of the 11 clusters found. As expected, the diffuse emission from all six systems is contaminated by point sources to some degree, and for half of them active galactic nucleus emission dominates. X-ray follow-up observations will thus be crucial in order to establish robust cluster luminosities for eMACS clusters. Although the small number of distant X-ray luminous clusters in the MDS does not allow us to make firm predictions for the over 20 000 deg2 of extragalactic sky covered by eMACS, the identification of two extremely promising eMACS cluster candidates at z 0.6 (both yet to be observed with Chandra) in such a small solid angle is encouraging. Representing a tremendous gain over the presently known two dozen such systems from X-ray, optical and Sunyaev-Zel'dovich cluster surveys combined, the sample of over 100 extremely massive clusters at z > 0.5 expected from eMACS would be invaluable for the identification of the most powerful gravitational lenses in the Universe, as well as for in-depth and statistical studies of the physical properties of the most massive galaxy clusters out to z ∼ 1.
Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 mu m in their spectral energy distributions, recently measured by the Spitzer Infrared ...Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for mu m-sized grains, with little discontinuity in the surface density of the mu m-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the mu m-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models.
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