Multicolor Photometry Research Articles

Thermal infrared and optical photometry of Asteroidal Comet C/2002 CE10

C/2002 CE10 is an object in a retrograde elliptical orbit with Tisserand parameter −0.853 indicating a likely origin in the Oort Cloud. It appears to be a rather inactive comet since no coma and only a very weak tail was detected during the past perihelion passage. We present multi-color optical photometry, lightcurve and thermal mid-IR observations of the asteroidal comet. With the photometric analysis in BVRI, the surface color is found to be redder than asteroids, corresponding to cometary nuclei and TNOs/Centaurs. The time-resolved differential photometry supports a rotation period of 8.19 ± 0.05 h. The effective diameter and the geometric albedo are 17.9 ± 0.9 km and 0.03 ± 0.01, respectively, indicating a very dark reflectance of the surface. The dark and redder surface color of C/2002 CE10 may be attribute to devolatilized material by surface aging suffered from the irradiation by cosmic rays or from impact by dust particles in the Oort Cloud. Alternatively, C/2002 CE10 was formed of very dark refractory material originally like a rocky planetesimal. In both cases, this object lacks ices (on the surface at least). The dynamical and known physical characteristics of C/2002 CE10 are best compatible with those of the Damocloids population in the Solar System, that appear to be exhaust cometary nucleus in Halley-type orbits. The study of physical properties of rocky Oort cloud objects may give us a key for the formation of the Oort cloud and the solar system.

The ALHAMBRA survey: 2D analysis of the stellar populations in massive early-type galaxies atz< 0.3

We present a technique that permits the analysis of stellar population gradients in a relatively low-cost way compared to integral field unit (IFU) surveys. We developed a technique to analyze unresolved stellar populations of spatially resolved galaxies based on photometric multi-filter surveys. This technique allows the analysis of vastly larger samples and out to larger galactic radii. We derived spatially resolved stellar population properties and radial gradients by applying a centroidal Voronoi tessellation and performing a multicolor photometry spectral energy distribution fitting. This technique has been successfully applied to a sample of 29 massive (M⋆> 1010.5M⊙) early-type galaxies atz< 0.3 from the ALHAMBRA survey. We produced detailed 2D maps of stellar population properties (age, metallicity, and extinction), which allow us to identify galactic features. Radial structures were studied, and luminosity-weighted and mass-weighted gradients were derived out to 2–3.5Reff. We find that the spatially resolved stellar population mass, age, and metallicity are well represented by their integrated values. We find the gradients of early-type galaxies to be on average flat in age (∇log AgeL= 0.02 ± 0.06 dex/Reff) and negative in metallicity (∇[Fe/H]L= −0.09 ± 0.06 dex/Reff). Overall,the extinction gradients are flat (∇Av= −0.03 ± 0.09 mag/Reff) with a wide spread. These results are in agreement with previous studies that used standard long-slit spectroscopy, and with the most recent IFU studies. According to recent simulations, these results are consistent with a scenario where early-type galaxies were formed through major mergers and where their final gradients are driven by the older ages and higher metallicity of the accreted systems. We demonstrate the scientific potential of multi-filter photometry to explore the spatially resolved stellar populations of local galaxies and confirm previous spectroscopic trends from a complementary technique.

Prospects of the “WSO-UV” Project for Star Formation Study in Nearby Dwarf Galaxies

In the present work we consider the questions of star formation and evolution of nearby dwarf galaxies. We describe the method of star formation history determination based on multicolor photometry of resolved stars and models of color-magnitude diagrams of the galaxies. We present the results of star formation rate determination and its dependence on age and metallicity for dwarf irregular and dwarf spheroidal galaxies in the two nearby galaxy groups M81 and Cen A. Similar age of the last episode of star formation in the central part of the M81 group and also unusually high level of metal enrichment in the several galaxies of the Cen A group are mentioned. We pay special attention to the consideration of perspectives of star formation study in nearby dwarf galaxies with he new WSO-UV observatory.

Connecting the progenitors, pre-explosion variability and giant outbursts of luminous blue variables with Gaia16cfr

We present multi-epoch, multi-colour pre-outburst photometry and post-outburst light curves and spectra of the luminous blue variable (LBV) outburst Gaia16cfr discovered by the Gaia satellite on 1 December 2016. We detect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases of 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging 13 years before outburst. Pre-outburst optical photometry is consistent with an 18 Msun F8 I star, although the star was likely reddened and closer to 30 Msun. The pre-outburst source exhibited a significant near-infrared excess consistent with a 120 AU shell with 4x10-6 Msun of dust. We infer that the source was enshrouded by an optically-thick and compact shell of circumstellar material from an LBV wind, which formed a pseudo-photosphere consistent with S Dor-like variables in their "maximum" phase. Within a year of outburst, the source was highly variable on 10-30 day timescales. The outburst light curve closely matches that of the 2012 outburst of SN 2009ip, although the observed velocities are significantly slower than in that event. In Halpha, the outburst had an excess of blueshifted emission at late times centred around -1500 km/s, similar to that of double-peaked Type IIn supernovae and the LBV outburst SN 2015bh. From the pre-outburst and post-outburst photometry, we infer that the outburst ejecta are evolving into a dense, highly structured circumstellar environment from precursor outbursts within years of the December 2016 event.

A Model of the Pulsating Extremely Low-mass White Dwarf Precursor WASP 0247–25B

Abstract We present an analysis of the evolutionary and pulsation properties of the extremely low-mass white dwarf precursor (B) component of the double-lined eclipsing system WASP 0247−25. Given that the fundamental parameters of that star have been obtained previously at a unique level of precision, WASP 0247−25B represents the ideal case for testing evolutionary models of this newly found category of pulsators. Taking into account the known constraints on the mass, orbital period, effective temperature, surface gravity, and atmospheric composition, we present a model that is compatible with these constraints and show pulsation modes that have periods very close to the observed values. Importantly, these modes are predicted to be excited. Although the overall consistency remains perfectible, the observable properties of WASP 0247−25B are closely reproduced. A key ingredient of our binary evolutionary models is represented by rotational mixing as the main competitor against gravitational settling. Depending on assumptions made about the values of the degree index ℓ for the observed pulsation modes, we found three possible seismic solutions. We discuss two tests, rotational splitting and multicolor photometry, that should readily identify the modes and discriminate between these solutions. However, this will require improved temporal resolution and higher S/N observations, which are currently unavailable.

MASTER OT J004207.99+405501.1/M31LRN 2015 luminous red nova in M31: discovery, light curve, hydrodynamics and evolution

We report the discovery and multicolor (VRIW) photometry of a rare explosive star MASTER OT J004207.99+405501.1 - a luminous red nova - in the Andromeda galaxy M31N2015-01a. We use our original light curve acquired with identical MASTER Global Robotic Net telescopes in one photometric system: VRI during first 30 days and W (unfiltered) during 70 days. Also we added publishied multicolor photometry data to estimate the mass and energy of the ejected shell, and discuss the likely formation scenarios of outbursts of this type. We propose the interpretation of the explosion, that is consistent with the evolutionary scenario where star merger is a natural stage of the evolution of close-mass stars and may serve as an extra channel for the formation of nova outbursts.

Multicolor photometry of geostationary objects

Multicolor photometry of geostationary objects

Rapid optical variations correlated with X-rays in the 2015 second outburst of V404 Cygni (GS 2023+338)

We present optical multi-colour photometry of V404 Cyg during the outburst from December, 2015 to January, 2016 together with the simultaneous X-ray data. This outburst occurred less than 6 months after the previous outburst in June-July, 2015. These two outbursts in 2015 were of a slow rise and rapid decay-type and showed large-amplitude ($\sim$2 mag) and short-term ($\sim$10 min-3 hours) optical variations even at low luminosity (0.01-0.1$L_{\rm Edd}$). We found correlated optical and X-ray variations in two $\sim$1 hour time intervals and performed Bayesian time delay estimations between them. In the previous version, the observation times of X-ray light curves were measured at the satellite and their system of times was Terrestrial Time (TT), while those of optical light curves were measured at the Earth and their system of times was Coordinated Universal Time (UTC). In this version, we have corrected the observation times and obtained a Bayesian estimate of an optical delay against the X-ray emission, which is $\sim$30 s, during those two intervals. In addition, the relationship between the optical and X-ray luminosity was $L_{\rm opt} \propto L_{\rm X}^{0.25-0.29}$ at that time. These features can be naturally explained by disc reprocessing.

On the assessment of the nature of open star clusters and the determination of their basic parameters with limited data

Our knowledge of stellar evolution and of the structure and chemical evolution of the Galactic disk largely builds on the study of open star clusters. Because of their crucial role in these relevant topics, large homogeneous catalogues of open cluster parameters are highly desirable. Although efforts have been made to develop automatic tools to analyse large numbers of clusters, the results obtained so far vary from study to study, and sometimes are very contradictory when compared to dedicated studies of individual clusters. In this work we highlight the common causes of these discrepancies for some open clusters, and show that at present dedicated studies yield a much better assessment of the nature of star clusters, even in the absence of ideal data-sets. We make use of deep, wide-field, multi-colour photometry to discuss the nature of six strategically selected open star clusters: Trumpler~22, Lynga~6, Hogg~19, Hogg~21, Pismis~10 and Pismis~14. We have precisely derived their basic parameters by means of a combination of star counts and photometric diagrams. Trumpler~22 and Lynga~6 are included in our study because they are widely known, and thus provided a check of our data and methodology. The remaining four clusters are very poorly known, and their available parameters have been obtained using automatic tools only. Our results are in some cases in severe disagreement with those from automatic surveys.

Photometric and Spectroscopic Observations of the Algol Type Binary V Triangle

Abstract Time-series, multi-color photometry and high-resolution spectra of the short-period eclipsing binary V Tri were obtained through observation. The completely covered light and radial velocity (RV) curves of the binary system are presented. All times of light minima derived from both photoelectric and CCD photometry were used to calculate the orbital period and new ephemerides of the eclipsing system. The analysis of the O − C diagram reveals that the orbital period is 0.58520481 days, decreasing at a rate of dP/dt = −7.80 × 10−8 day yr−1. The mass transfer between the two components and the light-time-travel effect due to a third body could be used to explain the period decrease. However, a semi-detached configuration with the lower-mass component filling and the primary nearly filling each of their Roche lobes was derived from the synthesis of the light and RV curves by using the 2015 version of the Wilson–Devinney code. We consider the period decrease to be the nonconservative mass transfer from the secondary component to the primary and the mass loss of the system, which was thought to be an EB type, while it should be an EA type (semi-detached Algol-type) from our study. The masses, radii, and luminosities of the primary and secondary are 1.60 ± 0.07 M ⊙, 1.64 ± 0.02 R ⊙, and 14.14 ± 0.73 L ⊙ and 0.74 ± 0.02 M ⊙, 1.23 ± 0.02 R ⊙, and 1.65 ± 0.05 L ⊙, respectively.

Kottamia 74-inch telescope discovery of the new eclipsing binary KAO-EGYPT J225702.44+523222.1.: First CCD photometry and light curve analysis

We present the first multicolor CCD photometry for the newly discovered binary system KAO-EGYPT J225702.44+523222.1. New times of light minimum and new ephemeris were obtained. The VR I light curves were analyzed using WD code, the difference in maximum light at phase 0.25 is modeled with a cool spot on the secondary component. The solution show that the system is A-subtype, overcontact binary with fill-out factor=42% and low mass ratio, q=0.275. The two components of spectral types K0 and K1 and the primary component is the massive one. The position of both components on the M-L and M–R relations revealed that the primary component is a main sequence star while the secondary is an evolved component.

PTF1 J085713+331843, a new post-common-envelope binary in the orbital period gap of cataclysmic variables

We report the discovery and analysis of PTF1 J085713+331843, a new eclipsing post common-envelope detached white-dwarf red-dwarf binary with a 2.5h orbital period discovered by the Palomar Transient Factory. ULTRACAM multicolour photometry over multiple orbital periods reveals a light curve with a deep flat-bottomed primary eclipse and a strong reflection effect. Phase-resolved spectroscopy shows broad Balmer absorption lines from the DA white dwarf and phase-dependent Balmer emission lines originating on the irradiated side of the red dwarf. The temperature of the DA white dwarf is $T_\mathrm{WD} = 25700 \pm 400\,$K and the spectral type of the red dwarf is M3-5. A combined modelling of the light curve and the radial velocity variations results in a white dwarf mass of $M_\mathrm{WD} = 0.61^{+0.18}_{-0.17}\, \mathrm{M_{\odot}}$ and radius of $R_\mathrm{WD} = 0.0175^{+0.0012}_{-0.0011}\, \mathrm{R_{\odot}}$, and a red dwarf mass and radius of $M_\mathrm{RD} = 0.19^{+0.10}_{-0.08}\, \mathrm{M_{\odot}}$ and $R_\mathrm{RD} = 0.24^{+0.04}_{-0.04}\, \mathrm{R_{\odot}}$. The system is either a detached cataclysmic variable or has emerged like from the common envelope phase at nearly its current orbital period. In $\sim70\,$Myr, this system will become a cataclysmic variable in the period gap.

On the nature of the candidate T-Tauri star V501 Aurigae★

We report new multi-colour photometry and high-resolution spectroscopic observations of the long-period variable V501 Aur, previously considered to be a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region. The spectroscopic observations reveal that V501 Aur is a single-lined spectroscopic binary system with a 68.8-day orbital period, a slightly eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of Taurus-Auriga. The photometry shows quasi-periodic variations on a different, ~55-day timescale that we attribute to rotational modulation by spots. No eclipses are seen. The visible object is a rapidly rotating (vsini ~ 25 km/s) early K star, which along with the rotation period implies it must be large (R > 26.3 Rsun), as suggested also by spectroscopic estimates indicating a low surface gravity. The parallax from the Gaia mission and other independent estimates imply a distance much greater than the Taurus-Auriga region, consistent with the giant interpretation. Taken together, this evidence together with a re-evaluation of the LiI~$\lambda$6707 and H$\alpha$ lines shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a giant primary far behind the Taurus-Auriga star-forming region. The large mass function from the spectroscopic orbit and a comparison with stellar evolution models suggest the secondary may be an early-type main-sequence star.

The K2-ESPRINT project. VI. K2-105 b, a hot Neptune around a metal-rich G-dwarf

Abstract We report on the confirmation that the candidate transits observed for the star EPIC 211525389 are due to a short-period Neptune-sized planet. The host star, located in K2 campaign field 5, is a metal-rich ([Fe/H] = 0.26 ± 0.05) G-dwarf (Teff = 5430 ± 70 K and log g = 4.48 ± 0.09), based on observations with the High Dispersion Spectrograph (HDS) on the Subaru 8.2 m telescope. High spatial resolution AO imaging with HiCIAO on the Subaru telescope excludes faint companions near the host star, and the false positive probability of this target is found to be <10−6 using the open source vespa code. A joint analysis of transit light curves from K2 and additional ground-based multi-color transit photometry with MuSCAT on the Okayama 1.88 m telescope gives an orbital period of P = 8.266902 ± 0.000070 d and consistent transit depths of Rp/R⋆ ∼ 0.035 or (Rp/R⋆)2 ∼ 0.0012. The transit depth corresponds to a planetary radius of $R_{\rm p} = 3.59_{-0.39}^{+0.44}\,R_{\oplus }$, indicating that EPIC 211525389 b is a short-period Neptune-sized planet. Radial velocities of the host star, obtained with the Subaru HDS, lead to a 3 σ upper limit of 90 M⊕ (0.00027 M⊙) on the mass of EPIC 211525389 b, confirming its planetary nature. We expect this planet, newly named K2-105 b, to be the subject of future studies to characterize its mass, atmosphere, and spin–orbit (mis)alignment, as well as investigate the possibility of additional planets in the system.

Multi-color simultaneous photometry of the T-Tauri star with planetary candidate, CVSO 30

Abstract We present three-band simultaneous observations of a weak-line T-Tauri star, CVSO 30 (PTFO 8-8695), which is one of the youngest objects having a candidate transiting planet. The data were obtained with the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets (MuSCAT) on the 188 cm telescope at Okayama Astrophysical Observatory in Japan. We observed the fading event in the $g^{\prime }_2$-, $r^{\prime }_2$-, and zs, 2-bands simultaneously. As a result, we find a significant wavelength dependence of fading depths of about 3.1%, 1.7%, and 1.0% for the three bands. A cloudless H/He-dominant atmosphere of a hot Jupiter cannot explain this large wavelength dependence. Additionally, we rule out a scenario with the occultation of the gravity-darkened host star. Thus our result is in favor of the fading origin as a circumstellar dust clump or occultation of an accretion hotspot.

SDSS J105754.25+275947.5: a period-bounce eclipsing cataclysmic variable with the lowest-mass donor yet measured

We present high-speed, multicolour photometry of the faint, eclipsing cataclysmic variable (CV) SDSS J105754.25+275947.5. The light from this system is dominated by the white dwarf. Nonetheless, averaging many eclipses reveals additional features from the eclipse of the bright spot. This enables the fitting of a parameterised eclipse model to these average light curves, allowing the precise measurement of system parameters. We find a mass ratio of q = 0.0546 $\pm$ 0.0020 and inclination i = 85.74 $\pm$ 0.21$^{\circ}$. The white dwarf and donor masses were found to be M$_{\mathrm{w}}$ = 0.800 $\pm$ 0.015 M$_{\odot}$ and M$_{\mathrm{d}}$ = 0.0436 $\pm$ 0.0020 M$_{\odot}$, respectively. A temperature T$_{\mathrm{w}}$ = 13300 $\pm$ 1100 K and distance d = 367 $\pm$ 26 pc of the white dwarf were estimated through fitting model atmosphere predictions to multicolour fluxes. The mass of the white dwarf in SDSS 105754.25+275947.5 is close to the average for CV white dwarfs, while the donor has the lowest mass yet measured in an eclipsing CV. A low-mass donor and an orbital period (90.44 min) significantly longer than the period minimum strongly suggest that this is a bona fide period-bounce system, although formation from a white dwarf/brown dwarf binary cannot be ruled out. Very few period-minimum/period-bounce systems with precise system parameters are currently known, and as a consequence the evolution of CVs in this regime is not yet fully understood.

The optical counterpart to the Be/X-ray binary SAX J2239.3+6116

The main goal of this work is to perform a detailed study of the optical variability of the Be/X-ray binary SAX J2239.3+6116. We obtained multi-colour BVRI photometry and polarimetry and 4000-7000 A spectroscopy. The optical counterpart to SAX J2239.3+6116 is a V=14.8 B0Ve star located at a distance of ~4.9 kpc. The interstellar reddening in the direction of the source is E(B-V)=1.70 mag. The monitoring of the Halpha line reveals a slow long-term decline of its equivalent width since 2001. The line profile is characterized by a stable double-peak profile with no indication of large-scale distortions. Although somewhat higher than predicted by the models, the optical polarization is consistent with electron scattering in the circumstellar disk. We attribute the long-term decrease in the intensity of the Halpha line to the dissipation of the circumstellar disk of the Be star. The longer variability timescales observed in SAX J2239.3+6116 compared to other Be/X-ray binaries may be explained by the wide orbit of the system.

Multi-site, multi-colour and space photometry of a southern δ Scuti star, 38 Eri

38 Eri is a δ Scuti star in the shell hydrogen burning stage of evolution, with a 0.04 mag peak-to-peak amplitude and a very complex light variation. It was discovered in 1971. In the subsequent investigation the star always showed a different frequency content. A ground-based multi-site campaign and a MOST observation were devoted to resolve the contradicting pulsational behaviour. We present the preliminary result of our investigation obtained on Stromgren b and MOST data. The complexity of the pulsation is confirmed, but the comprehensive analysis helps to resolve the frequencies of the fast rotating star.

Gaia's view of the λ Boo star puzzle

The evolutionary status of the chemically peculiar class of $\lambda$ Boo stars has been intensely debated. It is now agreed that the $\lambda$ Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle. We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry. We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing $\lambda$ Boo spectra. The relative importance of these channels varies with age, temperature and environment.

Visual Binary Stars: Data to Investigate Formation of Binaries

Abstract Statistics of orbital parameters of binary stars as well as statistics of their physical characteristics bear traces of star formation history. However, statistical investigations of binaries are complicated by incomplete or missing observational data and by a number of observational selection effects. Visual binaries are the most common type of observed binary stars, with the number of pairs exceeding 130 000. The most complete list of presently known visual binary stars was compiled by cross-matching objects and combining data of the three largest catalogues of visual binaries. This list was supplemented by the data on parallaxes, multicolor photometry, and spectral characteristics taken from other catalogues. This allowed us to compensate partly for the lack of observational data for these objects. The combined data allowed us to check the validity of observational values and to investigate statistics of the orbital and physical parameters of visual binaries. Corrections for incompleteness of observational data are discussed. The datasets obtained, together with modern distributions of binary parameters, will be used to reconstruct the initial distributions and parameters of the function of star formation for binary systems.