Infrared Light Curves Research Articles

Rotationally Resolved 8-35 Micron Spitzer Space Telescope Observations of the Nucleus of Comet 9P/Tempel 1

We have utilized the Spitzer Space Telescope (SST) Infrared Spectrograph (IRS) to directly observe thermal emission from the nucleus of comet 9P/Tempel 1 on UT 2004 March 25-27. We obtained 8-35 μm low-resolution (R ~ 100) spectra and contemporaneous 16 and 22 μm photometric imaging over a 39 hr period. The comet was 3.7 AU from the Sun at the time, approximately 464 days before perihelion on 2005 July 5, and showed no evidence of extended emission beyond a point source. Visual inspection of the absolute photometry implies a rotation period of 40 ± 2 hr, consistent with earlier results. Snapshot photometry by Spitzer at 8 and 24 μm, taken on UT 2004 March 10 and 15, respectively, are consistent with this light-curve phasing and with the IRS-measured flux. The spectra agree well with the predictions of the standard thermal model for a slowly rotating body with thermal inertia between 0 and 50 J K-1 m-2 s-1/2, and are inconsistent with any rapid rotator model. The mean effective radius at the middle of the light curve is 3.3 ± 0.2 km. The maximum-to-minimum flux ratio of 1.8 in the light curve is consistent with an axial ratio a/b of 3.2 ± 0.4, implying a = 7.2 ± 0.9 km and b = 2.3 ± 0.3 km. Combining our SST infrared light curve with visible observations of the nucleus, we obtain a visible geometric albedo of 0.04 ± 0.01. With this sized nucleus and the published water production rates, we estimate that 9% ± 2% of the surface area is actively emitting volatile material at perihelion.

Blue and infrared light curves of the mysterious pre-main-sequence star V582 Mon (KH 15D) from 1955 to 1970

In recent years, an increasing number of publications have been devoted to the peculiar and mysterious pre-main-sequence star V582 Mon, also known as KH 15D. This extraordinary T Tauri star, located in the young star cluster NGC 2264, appears to be an eclipsing variable. In the present paper, we report a unique and self-consistent set of light curves in the blue and near-infrared (IR) bands, spanning a 15-yr interval (epoch 1955–1970). Our photometric data show clearly that the beginning of the eclipse stage occurred in early 1958 in the blue, and perhaps around 4 yr later in the IR. The light-curve period turns out to be the same reported by recent observations (about 48.3 d), so that no evidence for a period change Results. On the other hand, in our data the light-curve shape appears to be sinusoidal and is therefore different from the one displayed today. The photometric behaviour, determined with time-series and colour-index analysis, suggests that V582 Mon (KH 15D) could initially be surrounded by an accretion disc/torus seen edge-on, with subsequent thin dust formation at the beginning of the blue radiation absorption. The dust could then aggregate into larger particles providing the transition between selective and total absorption, accompanied with eclipsing variability in the IR. The minima of the periodic light curve become deeper owing to the increasing dimension and number of dust grains, and then flatten owing to a contraction in the disc.

Multiwavelength Observations of the Galactic Black Hole Transient 4U 1543−47 during Outburst Decay: State Transitions and Jet Contribution

Multiwavelength observations of Galactic black hole (GBH) transients during state transitions and in the low/hard state may provide detailed information on the accretion structure of these systems. The object 4U 1543-47 is a GBH transient that was covered exceptionally well in X-rays and the infrared (daily observations) and reasonably well in the optical and radio during its outburst decay in 2002. When all the available information is gathered from the intermediate and the low/hard states, 4U 1543-47 makes an important contribution to our understanding of state transitions and the role of outflows in the high-energy emission properties of black hole binaries. The evolution of the X-ray spectral and temporal properties and the infrared light curve place strong constraints on different models to explain the overall emission from accreting black holes. The overall spectral energy distribution is consistent with a synchrotron origin for the optical and infrared emission; however, the X-ray flux is above the power-law continuation of the optical and infrared flux. The infrared light curve, the HEXTE light curve, and the evolution of the X-ray photon index indicate that the major source of hard X-rays cannot be direct synchrotron radiation from an acceleration region in a jet for most of the outburst decay.

The Liverpool telescope

AbstractThe Liverpool Telescope is a 2.0 metre robotic telescope on La Palma. It achieved first light in July 2003, and began science operations in January 2004, with (supervised) robotic operation from April 2004. Unmanned operation is planned for October 2004. As a national, common‐user facility, the telescope must support over 50 science programmes and is equipped both with common user and experiment specific instruments. As an example, the SupIRCam instrument has been designed to obtain infrared light curves of Type Ia supernovae. This instrument achieved first light in July 2004. From August 2004 the telescope participates in the ROBONET‐1.0 network of 2.0 metre telescopes with the Faulkes Telescopes located in Hawaii and Australia, executing coordinated observations of GRB and exoplanet microlensing events. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The 2002 Outburst of the Black Hole X‐Ray Binary 4U 1543−47: Optical and Infrared Light Curves

We have obtained simultaneous optical and near infrared observations of 4U 1543-47 during its 2002 outburst. The most striking feature of the outburst light curve is the secondary maximum which appears after the object transitions into the low-hard state. This secondary maximum is much stronger in the infrared bands than optical. We suggest that the origin of the secondary maximum flux may be synchrotron radiation associated with a jet. Close infrared monitoring may lead to reliable triggers for simultaneous multiwavelength campaigns to study jet formation processes.

The fundamental parameters of the Algol binary AI Draconis revisited

We present the results of an analysis of our infrared light curves of the Algol-type binary AI Draconis in the J, H and K bands, and of published light curves in the B, V and Stromgren uvby bands, together with spectra obtained by us. The analysis of the light curves was carried out using a code based on atlas model atmospheres and Roche geometry. The small contribution of the secondary cool component to the total light of the system in the visible, producing light curves with very shallow secondary eclipses, makes the stellar and orbital parameters derived from light-curve analysis in the visible spectral range uncertain. The larger contribution of the secondary star to the infrared fluxes makes this range particularly well suited to the derivation of precise orbital and stellar parameters in binaries of Algol type. From the simultaneous solution of the infrared JHK light curves, we derive the following absolute orbital and stellar parameters for the two components: 〈Teff,1〉= 10 160 ± 160 K, Req,1= 2.12 ± 0.04 R⊙, log(〈g〉)1= 4.23; 〈Teff,2〉= 5586 ± 110 K, Req,2= 2.36 ± 0.04 R⊙, log(〈g〉)2= 3.76; M1= 2.86 ± 0.09 M⊙, q=M2/M1= 0.44 ± 0.03; a= 7.62 ± 0.09 R⊙, i= 76.53°± 0.3°, e≃ 0.0. Here, 〈Teff〉 and log(〈g〉) indicate average surface values, Req is the equivalent radius of the deformed star and a is the orbital size. In our light-curve solutions, the secondary star of AI Dra fills its Roche lobe (as also indicated by the spectroscopy), thus discounting claims, based on UBV light curves, that both components of the binary are located within their Roche lobes. The visible and infrared photometry show no evidence of any significant infrared excess in the system, and the distance of AI Dra is estimated as d= 169 ± 17 pc. Based on the spectra of AI Dra and template stars in the ranges 8210–9060, 6250–7130 and 4040–4920 A, we classify the stellar components of AI Dra and find that the most probable spectral types are A0V (or perhaps A1V) for the primary and F9.5V for the secondary (although it could reach as far as G4V), respectively. From our spectroscopic observations, the spectral evolution of AI Dra with orbital phase is also presented. Furthermore, we obtain the projected rotational velocity of the secondary, whose value turns out to be compatible with the star filling its Roche lobe.

Seasonality on terrestrial extrasolar planets: inferring obliquity and surface conditions from infrared light curves

We investigate the relationship between the seasonality of hypothetical terrestrial extrasolar planets and their infrared light curves. The moderate obliquity of the Earth leads to seasonal variation in insolation and surface temperatures and, consequently, the infrared radiation emitted to space. The orbital parameters of known extrasolar planets and planet formation theory suggest that terrestrial exoplanets may have more eccentric orbits and/or larger obliquities than that of the Earth. These planets will experience larger variations in stellar radiation: we propose that changes in the emitted infrared flux along the orbit might be detectable by a future planet-finding observatory and that orbital infrared light curves contains information about the obliquities and thermal properties of these objects complementary to other data (e.g., spectroscopy). We present an analytical energy balance model that includes both meridional heat transport and the thermal inertia of an ocean/atmosphere. We use this model to calculate infrared light curves for different obliquities, orbital eccentricities, and viewing geometries. We show that: (1) the infrared orbital variability of “blackbody” planets lacking atmospheres or oceans is comparable to the mean value; (2) the shape of the light curve is sensitive to the obliquity of a planet and the location of the equinoxes along the orbit; and (3) the light curve of an Earth-like planet with a global ocean and atmosphere is dramatically attenuated and shifted in phase relative to a blackbody planet. We investigate the distribution of infrared light curve amplitudes in a statistical ensemble of blackbody and Earth-like planets. We examine the question of light-curve uniqueness and conclude that to independently constrain the major parameters it will be necessary to measure the amplitude and phase of higher (suborbital) harmonics in the light curve. Alternatively, measurements of seasonally-varying parameters other than IR flux must be used.

The Infrared Counterpart of the X-Ray Nova XTE J1720—318

Abstract We report on the discovery of an infrared counterpart to the X-ray transient XTE J1720$-$318 on 2003 January 18, nine days after an X-ray outburst, and the infrared light curve during the first 130 days after the outburst. The infrared light curve shows a decline of $\sim 1.2 \,\mathrm{mag}$ from the peak magnitude of $K_\mathrm{s} \sim 15.3$ over the observation period, and a secondary maximum, about 40 days after the outburst. Another small increase in the flux was also recorded about 20 days after the outburst. These increases were also detected in the X-ray light curve. The $J H K_\mathrm{s}$ colors are consistent with an X-ray irradiated accretion disk suffering an extinction of $A_V \sim 8$, which is also inferred from its X-ray spectrum and the extinction map constructed from far-infrared dust emission of this line of sight. These $J, H$, and $K_\mathrm{s}$ observations demonstrate that useful data can be obtained even for such an object, which suffers heavy optical extinction, possibly located beyond the galactic center.

GRO J0422+32: The Lowest Mass Black Hole?

We have obtained optical and infrared photometry of the soft X-ray transient GRO J0422+32. From this photometry, we find a secondary star spectral type of M1, and an extinction of AV = 0.74 ± 0.09. We present the first observed infrared (J-, H-, and K-band) ellipsoidal variations, and model them with WD98, a recent version of the Wilson-Devinney light curve-modeling code. Assuming no significant contamination of the infrared light curves, we find a lower limit to the inclination angle of 43° corresponding to an upper limit on the mass of the compact object of 4.92 M☉. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 45° ± 2°. This inclination angle corresponds to a primary black hole mass of 3.97 ± 0.95 M☉. Thus, we contend that J0422+32 contains the lowest mass stellar black hole reported, and the first to have a measured mass that falls in the 3-5 M☉ range.

UBVJHKLM photometry of the symbiotic Mira V407 Cyg in 1998–2002

New results of UBV JHKLM photometry of the symbiotic Mira V407 Cyg performed in 1998–2002 are reported. In 2002, these observations were supplemented with RI observations and a search for rapid variability in the V band. The hot component of V407 Cyg experienced a strong flare in 1998, which was the second in the history of photometric observations of this star; this flare is still continuing. During the flare, the spectral energy distribution of the hot component can be approximated by blackbody radiation with a temperature of ∼7200 K. At the maximum brightness, the bolometric flux from the hot component did not exceed 3% of the Mira's mean bolometric flux, while its bolometric luminosity was ∼400L⊙. Appreciable variations of the star's BV brightness \((\tilde0\mathop m\limits_. 7)\) on a timescale of several days have been observed. These variations are not correlated with variations of B-V. Flickering on a timescale of several minutes with an amplitude of \(\tilde0\mathop m\limits_. 2\) has been detected in the V band. The observations suggest that the hot component can be in three qualitatively different states. In a model with a rapidly rotating white dwarf, these states can be associated with (i) the quiescent state of the white dwarf (with a very low accretion rate), (ii) an ejection state, and (iii) an accretion state. The Mira pulsation period P is \( \approx 762\mathop d\limits_. 9\), with its infrared maximum occurring ∼0.15P after the visual maximum. A “step” is observed on the ascending branch of the Mira infrared light curves. In 1998, the gradual increase of the mean K brightness of the Mira that had been observed since 1984 was interrupted by an unusually deep minimum, after which the mean level of the K brightness considerably decreased.

Light curve interpretation for “Quiescent” X-ray novae in a model with noncollisional interaction between the flow and disk. The system GU Mus = GRS 1124-68

We have analyzed optical and infrared light curves of GU Mus obtained during the system's quiescent state and carried out computations for “hot-line” and “hot-spot” models. The hot-line model describes the optical variability of GU Mus better than the hot-spot model. Season-to-season variations of the shape, amplitude, and mean levels of the optical and infrared light curves of GU Mus are due to changing parameters of the hot line and, to a lesser degree, of the accretion disk. Taking into account the contribution of the variability of the disk + hot line system to the variability of the system as a whole, we are able to reliably estimate the orbital inclination, \(i = 54^\circ \pm 1^\circ .3\), and the mass of the black hole, MX=(6.7–7.6)M⊙.

Modeling the Remarkable Multiwavelength Light Curves of EF Eridanus: The Detection of Its Irradiated Brown Dwarf-like Secondary Star

We present optical and infrared phase-resolved photometry of the magnetic cataclysmic variable EF Eri during a low state. The BVRIJ light curves are very similar in appearance; all exhibit a dip of a few tenths of a magnitude near binary orbital phase 0.5. In contrast, however, the H- and K-band light curves show very large modulations, with maxima at orbital phase 0.5. We show that these modulations are not due to ellipsoidal variations but to the reflection/heating of one face of the very cool secondary star by the white dwarf primary. We find that the dips in the BVRIJ light curves are best modeled by a single hot spot on the white dwarf primary that is self-eclipsed once per orbit. By using an orbital inclination of i =4 5 � , we find the colatitude of the hot spot is 35 � � 10 � , its temperature is 12,000 K, and its radius is 29 � � 15 � . To explain the larger minimum seen in the J-band light curve requires that � 20% of the observed flux be supplied by an additional source of luminosity, which we believe is residual cyclotron emission. To model the observed amplitudes in the H- and K-band light curves requires a very cool irradiated brown dwarf–like secondary star with temperature Teff � 900 K (for i =4 5 � ). The irradiated side of this secondary star, however, has Teff d 1600 K. We present a new K-band spectrum of EF Eri that is consistent with this result. To properly model the light curve of EF Eri will require the incorporation of brown dwarf atmospheres into the WilsonDivinney program, as well as better estimates for the irradiated limb-darkening coefficients and albedos of such objects. Finally, we present a three-dimensional hydrodynamic model for EF Eri that demonstrates that the accretion stream from the secondary star is almost fully controlled by the magnetic field of the white dwarf primary. This model predicts that the narrow dips observed in the high-state infrared light curves of EF Eri, which nominally should lead the binary in orbital phase, can occur very close to phase 0.0, as required by our light-curve modeling.

The Optical/Near‐Infrared Light Curves of SN 2002ap for the First 140 Days after Discovery

Supernova (SN) 2002ap in M74 was observed in the $UBVRIJHK$ bands for the first 40 days following its discovery (2002 January 29) until it disappeared because of solar conjunction, and then in June after it reappeared. The magnitudes and dates of peak brightness in each band were determined. While the rate of increase of the brightness before the peak is almost independent of wavelength, the subsequent rate of decrease becomes smaller with wavelength from the $U$ to the $R$ band, and is constant at wavelengths beyond $I$. The photometric evolution is faster than in the well-known ``hypernovae'' SNe~1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The bolometric light curve of SN 2002ap for the full period of observations was constructed. The absolute magnitude is found to be much fainter than that of SN 1998bw, but is similar to that of SN 1997ef, which lies at the faint end of the hypernova population. The bolometric light curve at the early epochs was best reproduced with the explosion of a C+O star that ejects $2.5~M_\sun$ with kinetic energy $E_{\rm K}=4\times 10^{51}~{\rm ergs}$. A comparison of the predicted brightness of SN 2002ap with that observed after solar conjunction may imply that $\gamma$-ray deposition at the later epochs was more efficient than in the model. This may be due to an asymmetric explosion.

Interpreting the Evolving Clumpy Shell Structure of IRC +10216 in Terms of Time Dependent Dust Shell Models

The prototypical dust-enshrouded carbon Mira IRC +10216 is known to exhibit intrinsic changes on a time scale of the order of only a few years as revealed, e.g., by CO infrared line profiles (Winters et al. 2000a), its infrared light curves, and by high spatial resolution monitoring in the infrared (Osterbart et al. 2000; Tuthill et al. 2000). In particular, the infrared light curves indicate a possible periodicity on a ≈ 20 yr time scale, i.e. that a recurrent phenomenon might lead to the observed variations. Such multi-periodicity time scales of several (≈ 10) stellar pulsation periods are predicted by consistent hydrodynamical models which include a proper treatment of dust formation (e.g. Winters et al. 2000b). In these models discrete dust layers form in time intervals which are several times longer than the typical pulsation period of an AGB star (Fleischer, Gauger, & Sedlmayr 1995; Höfner, Feuchtinger, & Dorfi 1995).

K-band observations of WZ Sagittae during quiescence

We present high-speed K-band photometry of WZ Sge obtained 2 yr before the recent 2001 superoutburst. Our data show the first ever detection of a disc eclipse in WZ Sge during quiescence. Analysis of the ingress and egress times of the disc and bright spot gives constraints on the system parameters of M1 = 0.740 ± 0.071 M � , M2 = 0.0445 ± 0.0027 M � and i = 75. ◦ 89 ± 0. 32. Oscillations at 27.88 s ± 0.01 s and 28.61 s ± 0.01 s are present in the infrared light curve. We determine the infrared oscillation parameters and discuss the source of the oscillations. We analyse the long-term brightness variation in the K-band light curves and find no evidence for a precessing, elliptical accretion disc in quiescence.

Infrared light curves and absolute stellar parameters of the Algol system Librae: is Librae really an overmassive Algol binary?

We present the first infrared (IR) light curves in the J, H and K bands of δ Lib obtained at different observing runs from 1994 to 1998. These IR light curves, showing a secondary minimum much deeper than in visual bands, have been analysed in order to determine a new set of physical parameters. A new program using the Roche geometry, and stellar surface brightness from ATLAS model atmospheres, has been used in the analysis and allows us to determine the physical parameters and the distance of the binary. We compare these results with the Hipparcos parallax, with the spectroscopic masses of the components derived from the radial velocity curves, and with evolutionary stellar model predictions. The adoption of a mass M1≃ 2.85 M⊙ for the primary star would remove the discrepancies between our results and the Hipparcos distance, and the unusual location of the δ Lib components in the Teff− log g diagram. Our photometric analysis suggests that the stellar masses in δ Lib could be overestimated, casting doubt on the claim that the primary component of the system is overmassive and oversized compared with single main-sequence stars of similar masses.

Infrared colours for Mira-like long-period variables found in the Catalogue

Near-infrared, JHKL, photometry is presented for 193 Mira and semi-regular variables that were observed by Hipparcos; periods, bolometric magnitudes and amplitudes are derived for 92 of them. Because of the way in which the Hipparcos targets were selected, this group of stars provides a useful data base of Miras with low mass-loss rates Various period–colour relationships are discussed in detail. The colour, particularly at a given period is found to depend on the pulsation amplitude of the star. A comparison with models suggests that this is a consequence of atmospheric extension, in the sense that large-amplitude pulsators have very extended atmospheres and redder and but bluer than their lower amplitude counterparts. The stars with very extended atmospheres also have higher values of and hence higher mass-loss rates. This finding provides further evidence for the causal connection between pulsation and mass loss. Two sequences are identified in the versus log P diagram (where Hp is the Hipparcos broad-band magnitude) at short periods At a given period these two groups have, on average, the same pulsation amplitude, but different JHKL colours and spectral types. The short-period stars in the bluer sequence have similar near-infrared colours to the Miras found in globular clusters. Long-term trends in the infrared light curves are discussed for stars that have sufficient data.

An early-time infrared and optical study of the Type Ia Supernova 1998bu in M96

We present first-season infrared (IR) and optical photometry and spectroscopy of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of this event. SN 1998bu is one of the closest type Ia supernovae of modern times, and the distance of its host galaxy is well determined. We find that SN 1998bu is both photometrically and spectroscopically normal. However, the extinction to this event is unusually high, with A(V) = 1.0 +/- 0.11. We find that SN 1998bu peaked at an intrinsic M-V = -19.37 +/- 0.23. Adopting a distance modulus of 30.25 (Tanvir et al.) and using Phillips et al.'s relations for the Hubble constant, we obtain H-0 = 70.4 +/- 4.3 km s(-1) Mpc(-1). Combination of our IR photometry with those of Jha et al. provides one of the most complete early-phase IR light curves for a SN Ia published so far. In particular, SN 1998bu is the first normal SN Ia for which good pre-t(Bmax) IR coverage has been obtained. It reveals that the J, H and K light curves peak about 5 days earlier than the flux in the B-band curve.

Infrared Light Curves of Mira Variable Stars from [ITAL]COBE[/ITAL] DIRBE Data

We have used the COBE DIRBE database to derive near- and mid-infrared light curves for a well-defined sample of 38 infrared-bright Mira variable stars, and compared with optical data from the AAVSO. In general, the 3.5 micron and 4.9 micron DIRBE bandpasses provide the best S/N light curves, with S/N decreasing with wavelength at longer wavelengths. At 25 microns, good light curves are only available for ~10 percent of our stars, and at wavelengths >= 60 microns, extracting high quality light curves is not possible. The amplitude of variability is typically less in the near-infrared than in the optical, and less in the mid-infrared than in the near-infrared, with decreasing amplitude with increasing wavelength. On average, there are 0.20 +/- 0.01 magnitudes variation at 1.25 microns and 0.14 +/- 0.01 magnitudes variation at 4.9 micron for each magnitude variation in V. The observed amplitudes are consistent with results of recent theoretical models of circumstellar dust shells around Mira variables. For a few stars in our sample, we find clear evidence of time lags between the optical and maxima of phase ~ 0.05 - 0.13, with no lags in the minima. For three stars, mid-infrared maximum appears to occur slightly before that in the near-infrared,but after optical maximum. We find three examples of secondary maxima in the rising portions of the DIRBE light curves, all of which have optical counterparts in the AAVSO data, supporting the hypothesis that they are due to shocks rather than newly-formed dust layers. We find no conclusive evidence for rapid (hours to days) variations in the infrared brightnesses of these stars.

The Liverpool Telescope

The Liverpool Telescope is a 2.0 metre robotic telescope on La Palma. It achieved first light in July 2003, and began science operations in January 2004, with (supervised) robotic operation from April 2004. Unmanned operation is planned for October 2004. As a national, common-user facility, the telescope must support over 50 science programmes and is equipped both with common user and experiment specific instruments. As an example, the SupIRCam instrument has been designed to obtain infrared light curves of Type Ia supernovae. This instrument achieved first light in July 2004. From August 2004 the telescope participates in the ROBONET-1.0 network of 2.0 metre telescopes with the Faulkes Telescopes located in Hawaii and Australia, executing coordinated observations of GRB and exoplanet microlensing events. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)