Photometric Telescope Research Articles

Compact planetary nebulae: improved IR diagnostic criteria based on classification tree modelling

Abstract Planetary nebulae (PNe) are strong H α line emitters and a lot of new PNe discoveries have been made by the SuperCOSMOS AAO/UKST H α Survey (SHS) and the Isaac Newton Telescope Photometric H α Survey (IPHAS). However, their resulting list of candidates turned out to be heavily contaminated from H α-line mimics like young stellar objects (YSOs) and/or H ii regions. The aim of this work is to find new infrared criteria that can better distinguish compact PNe from their mimics using a machine learning approach and the photometric data from the Two-Micron All-Sky Survey and Wide-field Infrared Survey Explorer. Three classification tree models have been developed with the following colour criteria: W1 − W4 ≥ 7.87 and J − H < 1.10; H − W2 ≥ 2.24 and J − H < 0.50; and Ks− W3 ≥ 6.42 and J − H < 1.31 providing a list of candidates, characterized by a high probability to be genuine PNe. The contamination of this list of candidates from H α mimics is low but not negligible. By applying these criteria to the IPHAS list of PN candidates and the entire IPHAS and VPHAS+ DR2 catalogues, we find 141 sources, from which 92 are known PNe, 39 are new very likely compact PNe (without an available classification or uncertain) and 10 are classified as H ii regions, Wolf–Rayet stars, AeBe stars, and YSOs. The occurrence of false-positive identifications in this technique is between 10 and 15 per cent.

The Case for a Large-scale Occultation Network

Abstract We discuss the feasibility of and present initial designs and approximate cost estimates for a large (N ∼ 2000) network of small photometric telescopes that is purpose-built to monitor V ≲ 15 Gaia mission program stars for occultations by minor solar system bodies. The implementation of this network would permit measurement of the solar system’s tidal gravity field to high precision, thereby revealing the existence of distant trans-Neptunian objects such as the proposed “Planet Nine.” As a detailed example of the network capabilities, we investigate how occultations by Jovian Trojans can be monitored to track the accumulation of gravitational perturbations, thereby constraining the presence of undetected massive solar system bodies. We also show that the tidal influence of Planet Nine can be discerned from that of smaller, nearer objects in the Kuiper Belt. Moreover, ephemerides for all small solar system bodies observed in occultation could be significantly improved using this network, thereby improving spacecraft navigation and refining solar system modeling. Finally, occultation monitoring would generate direct measurements of size distributions for asteroid populations, permitting a better understanding of their origins.

On the properties of the magnetic Chemically Peculiar B, A, and F-type stars

AbstractWe present a preliminary analysis of the Strömgren uvby photometry of the magnetic CP stars obtained using the Four College Automated Photometric Telescope for its 21.5 years of operation ending in Fall 2012. We summarize the photometry for all the FCAPT mCP stars that have been published to date. We do not find any significant correlation between the amplitudes of variation in the uvby filters and the periods. A small number of stars show anomalous behaviour of the v filter which will be discussed in a future study.

Recovering the unsigned photospheric magnetic field from Ca II K observations

Context. A number of studies have aimed at defining the exact form of the relation between magnetic field strength and Ca II H and K core brightness. All previous studies have however been restricted to isolated regions on the solar disc or to a limited set of observations.Aims. We reassess the relationship between the photospheric magnetic field strength and the Ca II K intensity for a variety of surface features as a function of the position on the disc and the solar activity level. This relationship can be used to recover the unsigned photospheric magnetic field from images recorded in the core of Ca II K line.Methods. We have analysed 131 pairs of high-quality, full-disc, near-co-temporal observations from the Helioseismic and Magnetic Imager (SDO/HMI) and Precision Solar Photometric Telescope (Rome/PSPT) spanning half a solar cycle. To analytically describe the observationally determined relation, we considered three different functions: a power law with an offset, a logarithmic function, and a power-law function of the logarithm of the magnetic flux density. We used the obtained relations to reconstruct maps of the line-of-sight component of the unsigned magnetic field (unsigned magnetograms) from Ca II K observations, which were then compared to the original magnetograms.Results. We find that both power-law functions represent the data well, while the logarithmic function is good only for quiet periods. We see no significant variation over the solar cycle or over the disc in the derived fit parameters, independently of the function used. We find that errors in the independent variable, which are usually not accounted for, introduce attenuation bias. To address this, we binned the data with respect to the magnetic field strength and Ca II K contrast separately and derived the relation for the bisector of the two binned curves. The reconstructed unsigned magnetograms show good agreement with the original ones. Root mean square differences are less than 90 G. The results were unaffected by the stray-light correction of the SDO/HMI and Rome/PSPT data.Conclusions. Our results imply that accurately processed and calibrated Ca II K observations can be used to reconstruct unsigned magnetograms by using the relations derived in our study.

First photometric investigations of three eclipsing binaries: AST19571, AST21541, and AST38503

AST3-1 is the second-generation optical photometric telescope at Dome A in Antarctica. In this study, photometric solutions of three eclipsing binaries comprising AST19571, AST21541, and AST38503 were determined for the first time using the light curves obtained with AST3-1. The light curves for the three binaries in the Galactic disk field were analyzed with the Wilson–Devinney method. We found that AST19571 and AST21541 are intermediate-contact binary systems with fill-out factors of f=39.9(±5.4)% and 36.4( ± 4.7) %, respectively, and their mass ratios were determined as q=0.275(±0.0034) and 0.25( ± 0.0024). AST38503 was shown to be a deep-contact binary system with a degree of contact of f=66(±33)% and a mass ratio of q=0.314(±0.03). Some light minimum times were derived for the three contact binary stars. The results showed that the period of AST19571 is increasing at a rate of dp/dt=+4.71×10−7. This increase in the period could be explained by mass transfer between the components. The absolute parameters were estimated for the components of the three binaries.

On the variability of the A0 supergiants 9 Per, HR 1035, 13 Mon, Deneb, and HR 8020 as seen in FCAPT Strömgren photometry

We present differential Strömgren uvby Four College Automated Photometric Telescope (FCAPT) observations of five supergiants with spectral types near A0. For three stars we supplemented our new data with our earlier published data, and for two more stars we present new data. We used two computer programs Period04 and VStar in attempts to determine if significant periodicities are present. Some periods we found may not be real as their yearly coverages are only less about four months. Five years of 9 Per photometry and 11 years of HR 8020 photometry both suggest a period of 248 days which is 2/3 of a year. 13 Mon and HR 1035 may be variable, but the data we have taken does not permit us to determine their periods. Our most complete datasets for Deneb and for HR 8020 indicate very complex variability. This is not unexpected for stars with atmospheres where convection is the dominant mode of energy transportation. Among our five supergiants, 13 Mon has the smallest amplitudes for u, v, b, and y. Better sets of photometry for these stars require observing seasons to be as long as possible and should cover many observations per night rather than one. This should remove any effects of data being undersampled.

Studies of FCAPT uvby Photometry with Period04: The mCP Stars HD 5797, HD 36792, HD 27309, HD 47913, HD 74521, HD 120198, HD 171263, and HD 215441

We present differential Strömgren uvby Four College Automated Photometric Telescope (FCAPT) observations of eight magnetic chemically peculiar stars: HD 5797, HD 26792, HD 27309, HD 49713, HD 74521, HD 120198, HD 171263, and HD 215441. Our data sets are larger than those of most mCP stars in the literature. These are the first FCAPT observations of HD 5797, HD 26792, HD 49713, and HD 171263. Those for the other four stars substantially extend published FCAPT data sets. The FCAPT has observed some stars for a longer time range and with greater accuracy than other optical region telescopes. We determine very accurate periods and u, v, b, and y amplitudes, as well as if there are any long-term periods. Further, we compare our results with those of magnetic field measurements, when they exist, to help interpret the light curves. For each star, we used the Period04 computer program to analyze the uvby light curves. This program provides errors for the derived quantities. Our derived periods of 68.0457 ± 0.0200 days for HD 5797, 3.80205 ± 0.00015 days for HD 26792, 1.5688908 ± 0.0000046 days for HD 27309, 2.135361 ± 0.000031 days for HD 49713, 7.05053 ± 0.00024 for days HD 74521, 1.3857690 ± 0.0000058 days for HD 120198, 3.99744 ± 0.00015 days for HD 171263, and 9.487792 ± 0.000049 days for HD 215441 are refinements of the last determinations in the literature. We also found a low-frequency term for HD 49713 in all four filters.

NASA Data Used to Discover Eighth Planet Circling Distant Star

Discovering the origins of life and colonizing extraterrestrial planets are two of the greatest ambitions that the international scientific community has today. Today, NASA is more prepared than ever to embark on an unprecedented race to conquer other worlds. The Kepler mission, named after Johannes Kepler, the German astronomer of the 16th-17th centuries, was scheduled to begin on March 7, 2009. In this mission, Space Agency released space from the Cape Canaveral Air Force Base, Florida, a Delta II rocket that will carry the Kepler space probe. It will try to identify Earth-like planets that orbitate stars similar to the Sun in a warm area of space, with liquid water and oxygen, that is, heavenly bodies that have all the conditions of life formation and maintenance. Kepler is looking for a new Earth. Kepler is a critical component of NASA's efforts to identify and study planets with Earth-like eco-conditions. The results of the Kepler space photometer will prove to be extremely important in understanding the frequency of Earth-sized planets in our galaxy. They will also plan future missions to directly detect and investigate such worlds near neighboring stars. Although more than 300 planets outside the solar system have already been identified by similar investigation technologies, Kepler's power resides in the high sensitivity of its instruments to smaller, cooler, more hospitable and more like us planes than all those identified so far. Kepler has a special telescope on board, which will study 100,000 astronomers from the Cygnus-Lyra region of the Milky Way for more than three and a half years. Scientists expect to discover hundreds of planets as large as the Earth or even larger, located at different distances from their stars. the number of Earth-sized planets that have the potential to sustain life and be habitable of humans is great, Kepler could discover dozens of such celestial bodies; if they are rare, they may not discover any. If we find that most stars have Earths, this implies that life development can be a common issue through our galaxy, says William Borucki, principal investigator at NASA's California Ames Research Center. Discovery of only a few or a small number could indicate that we are alone in the Universe, the scientist added. Kepler's mission, according to the original English Kepler Mission, is a space mission, a cosmic station, a special cosmic ship and a space-based photometric telescope created and conducted by NASA to search for Terra planets in other solar systems. The Kepler cosmic station will observe and record the glow of more than 100,000 stars about 3-4 years in length to detect the periodic transition of a star's planets, a process of detecting the stars of a certain star called the transition method. The space mission is named in honor of German astronomer Johannes Kepler. A planet earth or a terrestrial planet in contrast to gaseous planets is a planet composed of rocks and metals that generally have three concentric shells (core or core, shell and bark or crust).

Mapping the three-dimensional dust extinction towards the supernova remnant S147 – the S147 dust cloud

We present a three dimensional (3D) extinction analysis in the region toward the supernova remnant (SNR) S147 (G180.0-1.7) using multi-band photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC), 2MASS and WISE. We isolate a previously unrecognised dust structure likely to be associated with SNR S147. The structure, which we term as "S147 dust cloud", is estimated to have a distance $d$ = 1.22 $\pm$ 0.21 kpc, consistent with the conjecture that S147 is associated with pulsar PSR J0538 + 2817. The cloud includes several dense clumps of relatively high extinction that locate on the radio shell of S147 and coincide spatially with the CO and gamma-ray emission features. We conclude that the usage of CO measurements to trace the SNR associated MCs is unavoidably limited by the detection threshold, dust depletion, and the difficulty of distance estimates in the outer Galaxy. 3D dust extinction mapping may provide a better way to identify and study SNR-MC interactions.

On the Photometric Variability of Very Sharp-lined Cool mCP Stars

We investigate the photometric variability of very sharp-lined cool mCP stars from a list published in 1970 by Dr. George W. Preston who suggested that some belonged to the long-period tail of the period distribution. In this study, we discuss our Strömgren uvby observations obtained with the Four College Automated Photometric Telescope (FCAPT) at the Fairborn Observatory for 22 of the stars in Preston’s list. We improved the periods of 11 stars. Further, we discuss results from the literature concerning the light, magnetic, and spectrum variability of these stars. Eleven of the stars are found to have periods longer than 20 days, and all but one of these stars display variations in the u and v filters that cannot be explained by the simple oblique rotator theory. We discuss some possible causes of this behavior.

Pushing the limits: detecting H2 emission from faint bipolar planetary nebulae in the IPHAS sample

We have obtained deep narrowband images in the near-infrared H2 (2.122 microns) emission line for a sample of 15 faint Isaac Newton Telescope Photometric Halpha Survey (IPHAS) bipolar planetary nebulae (PNe) to search for molecular material. H2 emission is found in most of them (14 out of 15), mostly associated with rings at their equatorial regions and with their bipolar lobes. These detections add to the high occurrence of H2 emission among bipolar PNe reported in previous works, resulting from the large reservoir of molecular material in these sources and the suitable excitation conditions for H2 emission. The correlation between detailed bipolar morphology and H2 luminosity is also confirmed: bipolar PNe with broad equatorial rings (R-BPNe) have almost no continuum emission, are H2 brighter and have larger H2/Brgamma line ratio than bipolar PNe with pinched equatorial waists (W-BPNe). The origin of this dichotomy is unclear. The larger size and age of R-BPNe are consistent with shock excitation of H2, whereas ultraviolet pumping is most likely the excitation mechanism in the smaller and younger W-BPNe, which would explain their lower H2 luminosity. Although both types of bipolar PNe seem to proceed from the same progenitor population, this does not imply that R-BPNe descend from W-BPNe. Otherwise, we note that some of the H2-weak bipolar PNe harbor post-common envelope binary systems and symbiotic stars. Finally, we suggest that the long-living H2 emission from R-BPNe arises from a discrete distribution of compact knots embedded within the ionized gas at the equatorial region.

Interacting large-scale magnetic fields and ionized gas in the W50/SS433 system

The W50/SS433 system is an unusual Galactic outflow-driven object of debatable origin. We have used the Australia Telescope Compact Array (ATCA) to observe a new 198 pointing mosaic, covering $3^\circ \times 2^\circ$, and present the highest-sensitivity full-Stokes data of W50 to date using wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We also present a complementary H$\alpha$ mosaic created using the Isaac Newton Telescope Photometric H$\alpha$ Survey of the Northern Galactic Plane (IPHAS). The magnetic structure of W50 is found to be consistent with the prevailing hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR), that has been re-energised by the jets from SS433. We observe strong depolarization effects that correlate with diffuse H$\alpha$ emission, likely due to spatially-varying Faraday rotation measure (RM) fluctuations of $\ge48$ to 61 rad m$^{-2}$ on scales $\le4.5$ to 6 pc. We also report the discovery of numerous, faint, H$\alpha$ filaments that are unambiguously associated with the central region of W50. These thin filaments are suggestive of a SNR's shock emission, and almost all have a radio counterpart. Furthermore, an RM-gradient is detected across the central region of W50, which we interpret as a loop magnetic field with a symmetry axis offset by $\approx90^{\circ}$ to the east-west jet-alignment axis, and implying that the evolutionary processes of both the jets and the SNR must be coupled. A separate RM-gradient is associated with the termination shock in the Eastern ear, which we interpret as a ring-like field located where the shock of the jet interacts with the circumstellar medium. Future optical observations will be able to use the new H$\alpha$ filaments to probe the kinematics of the shell of W50, potentially allowing for a definitive experiment on W50's formation history.

Variable Stars Observed in the Galactic Disk by AST3-1 from Dome A, Antarctica

Abstract AST3-1 is the second-generation wide-field optical photometric telescope dedicated to time-domain astronomy at Dome A, Antarctica. Here, we present the results of an i-band images survey from AST3-1 toward one Galactic disk field. Based on time-series photometry of 92,583 stars, 560 variable stars were detected with i magnitude ≤16.5 mag during eight days of observations; 339 of these are previously unknown variables. We tentatively classify the 560 variables as 285 eclipsing binaries (EW, EB, and EA), 27 pulsating variable stars (δ Scuti, γ Doradus, δ Cephei variable, and RR Lyrae stars), and 248 other types of variables (unclassified periodic, multiperiodic, and aperiodic variable stars). Of the eclipsing binaries, 34 show O’Connell effects. One of the aperiodic variables shows a plateau light curve and another variable shows a secondary maximum after peak brightness. We also detected a complex binary system with an RS CVn-like light-curve morphology; this object is being followed-up spectroscopically using the Gemini South telescope.

THREE TEMPERATE NEPTUNES ORBITING NEARBY STARS*

ABSTRACT We present the discovery of three modestly irradiated, roughly Neptune-mass planets orbiting three nearby Solar-type stars. HD 42618 b has a minimum mass of 15.4 ± 2.4 , a semimajor axis of 0.55 au, an equilibrium temperature of 337 K, and is the first planet discovered to orbit the solar analogue host star, HD 42618. We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 (ρ CrB). The new planet orbiting HD 164922 has a minimum mass of 12.9 ± 1.6 and orbits interior to the previously known Jovian mass planet orbiting at 2.1 au. HD 164922 c has a semimajor axis of 0.34 au and an equilibrium temperature of 418 K. HD 143761 c orbits with a semimajor axis of 0.44 au, has a minimum mass of 25 ± 2 , and is the warmest of the three new planets with an equilibrium temperature of 445 K. It orbits exterior to the previously known warm Jupiter in the system. A transit search using space-based CoRoT data and ground-based photometry from the Automated Photometric Telescopes (APTs) at Fairborn Observatory failed to detect any transits, but the precise, high-cadence APT photometry helped to disentangle planetary-reflex motion from stellar activity. These planets were discovered as part of an ongoing radial velocity survey of bright, nearby, chromospherically inactive stars using the Automated Planet Finder (APF) telescope at Lick Observatory. The high-cadence APF data combined with nearly two decades of radial velocity data from Keck Observatory and gives unprecedented sensitivity to both short-period low-mass, and long-period intermediate-mass planets.

Constraining the Galactic structure parameters with the XSTPS-GAC and SDSS photometric surveys

Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are used to derive the global structure parameters of the smooth components of the Milky Way. The data, which cover nearly 11,000 deg$^2$ sky area and the full range of Galactic latitude, allow us to construct a globally representative Galactic model. The number density distribution of Galactic halo stars is fitted with an oblate spheroid that decays by power law. The best-fit yields an axis ratio and a power law index $\kappa=0.65$ and $p=2.79$, respectively. The $r$-band differential star counts of three dwarf samples are then fitted with a Galactic model. The best-fit model yielded by a Markov Chain Monte Carlo analysis has thin and thick disk scale heights and lengths of $H_{1}=$ 322\,pc and $L_{1}=$2343\,pc, $H_{2}=$794\,pc and $L_{2}=$3638\,pc, a local thick-to-thin disk density ratio of $f_2=$11\,per\,cent, and a local density ratio of the oblate halo to the thin disk of $f_h=$0.16\,per\,cent. The measured star count distribution, which is in good agreement with the above model for most of the sky area, shows a number of statistically significant large scale overdensities, including some of the previously known substructures, such as the Virgo overdensity and the so-called "north near structure", and a new feature between 150\degr $< l < $ 240\degr~and $-1$5\degr $< b < $ $-$5\degr, at an estimated distance between 1.0 and 1.5\,kpc. The Galactic North-South asymmetry in the anticentre is even stronger than previously thought.

Method of Asteroid S/C Type Classification Using Color Indices

The color indices obtained from multi-color photometry have important significance of reference in the S/C type classification of asteroids, and the color parameter a derived from the principal component analysis of color indices is a key parameter of classification. Two methods, the direct demarcation at a = 0 and the cluster analysis of a-parameters, are applied to the asteroid S/C type classifications of the SDSSMOC4 and XSTPS-GAC (Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-Center) multi-color data samples, respectively. The results show that the two methods are effective and consistent in the case of large samples, and well consistent with the Carvano's result of S/C type classification, and that the a = 0 demarcation method is sensitive to the variation of sample space, but the method of cluster analysis is more stable.

SIX PLANETS ORBITING HD 219134

We present new, high-precision Doppler radial velocity (RV) data sets for the nearby K3V star HD 219134. The data include 175 velocities obtained with the HIRES Spectrograph at the Keck I Telescope, and 101 velocities obtained with the Levy Spectrograph at the Automated Planet Finder Telescope (APF) at Lick Observatory. Our observations reveal six new planetary candidates, with orbital periods of P=3.1, 6.8, 22.8, 46.7, 94.2 and 2247 days, spanning masses of msini=3.8, 3.5, 8.9, 21.3, 10.8 and 108 M_earth respectively. Our analysis indicates that the outermost signal is unlikely to be an artifact induced by stellar activity. In addition, several years of precision photometry with the T10 0.8~m automatic photometric telescope (APT) at Fairborn Observatory demonstrated a lack of brightness variability to a limit of ~0.0002 mag, providing strong support for planetary-reflex motion as the source of the radial velocity variations. The HD 219134 system, with its bright (V=5.6) primary provides an excellent opportunity to obtain detailed orbital characterization (and potentially follow-up observations) of a planetary system that resembles many of the multiple-planet systems detected by Kepler, and which are expected to be detected by NASA's forthcoming TESS Mission and by ESA's forthcoming PLATO Mission.

DETECTING THE COMPANIONS AND ELLIPSOIDAL VARIATIONS OF RS CVN PRIMARIES. II.oDRACONIS, A CANDIDATE FOR RECENT LOW-MASS COMPANION INGESTION

To measure the stellar and orbital properties of the metal-poor RS CVn binary o Draconis (o Dra), we directly detect the companion using interferometric observations obtained with the Michigan InfraRed Combiner at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array. The H-band flux ratio between the primary and secondary stars is the highest confirmed flux ratio (370 +/- 40) observed with long-baseline optical interferometry. These detections are combined with radial velocity data of both the primary and secondary stars, including new data obtained with the Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the Fred Lawrence Whipple Observatory and the 2-m Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We determine an orbit from which we find model-independent masses and ages of the components (M_A = 1.35 +\- 0.05 M_Sun, M_B = 0.99 +\- 0.02 M_Sun, system age = 3.0 -\+ 0.5 Gyr). An average of a 23-year light curve of o Dra from the Tennessee State University Automated Photometric Telescope folded over the orbital period newly reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations. The modeled light curve for our system's stellar and orbital parameters confirm these ellipsoidal variations due to the primary star partially filling its Roche lobe potential, suggesting most of the photometric variations are not due to stellar activity (starspots). Measuring gravity darkening from the average light curve gives a best-fit of beta = 0.07 +\- 0.03, a value consistent with conventional theory for convective envelope stars. The primary star also exhibits an anomalously short rotation period, which, when taken with other system parameters, suggests the star likely engulfed a low-mass companion that had recently spun-up the star.

PHOTOMETRIC TRENDS IN THE VISIBLE SOLAR CONTINUUM AND THEIR SENSITIVITY TO THE CENTER-TO-LIMB PROFILE

Solar irradiance variations over solar rotational time-scales are largely determined by the passage of magnetic structures across the visible solar disk. Variations on solar cycle time scales are thought to be similarly due to changes in surface magnetism with activity. Understanding the contribution of magnetic structures to total solar irradiance and solar spectral irradiance requires assessing their contributions as a function of disk position. Since only relative photometry is possible from the ground, the contrasts of image pixels are measured with respect to a center-to-limb intensity profile. Using nine years of full-disk red and blue continuum images from the Precision Solar Photometric Telescope at the Mauna Loa Solar Observatory (PSPT/MLSO), we examine the sensitivity of continuum contrast measurements to the center-to-limb profile definition. Profiles which differ only by the amount of magnetic activity allowed in the pixels used to determine them yield oppositely signed solar cycle length continuum contrast trends; either agreeing with the result of Preminger et al. (2011) showing negative correlation with solar cycle or disagreeing and showing positive correlation with solar cycle. Changes in the center-to-limb profile shape over the solar cycle are responsible for the contradictory contrast results, and we demonstrate that the lowest contrast structures, internetwork and network, are most sensitive to these. Thus the strengths of the full-disk, internetwork, and network photometric trends depend critically on the magnetic flux density used in the quiet-sun definition. We conclude that the contributions of low contrast magnetic structures to variations in the solar continuum output, particularly to long-term variations, are difficult, if not impossible, to determine without the use of radiometric imaging.

Evolutionary stages and disk properties of young stellar objects in the Perseus cloud

We investigated the evolutionary stages and disk properties of 211 young stellar objects (YSOs) across the Perseus cloud by modeling their broadband optical to mid-infrared (IR) spectral energy distribution (SED). Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC). About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage III phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index αexcess as determined for λ > λturnoff, and the disk inner radius Rin (determined from SED modeling) for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase with λturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at αexcess ≳ 0 and Rin ≳ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ ≲ 24 μm. About 23% of our YSO disks are classified as transitional disks, which have λturnoff ≥ 5.8 μm and Ldust/L★ > 10−3. The transitional disks and full disks occupy distinctly different regions on the Ldust/L★ vs. αexcess diagram. Taking Ldust/L★ as an approximate discriminator of disks with (>0.1) and without (<0.1) considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction with giant planets respectively. None of our transitional disks have αexcess (<0.0) or Ldust/L★ (>0.1) values that would otherwise be suggestive of disk clearing dominanted by grain growth.