Circumstellar Extinction Research Articles

Photometric activity of the Herbig Be star MWC 297 over 25 years

The photometric behavior of the hot, young Herbig Be star MWC 297 on various time scales is studied using published data, as well as new observations. The series of photometric observations covers about 25 years. Over this time, the star showed low-amplitude (ΔV ≈ 0.3 m ) irregular variability modulated by large-scale cyclic variability with an amplitude close to 0.2 m and a period (or quasi-period) of 5.4 ± 0.1 yr. A detailed seasonal analysis of the data shows that the light curve of MWC 297 displays two types of photometric features: low-amplitude Algol-like fading with an amplitude close to 0.2 m and low-amplitude flares resembling the flares of UV Ceti stars, but being more powerful and having longer durations. The variations of the stellar brightness are accompanied by variations of the B-V and V -R colors: when the brightness decreases, B-V decreases, while V -R increases (the star reddens). The reddening law is close to the standard interstellar reddening law. Although the character of the brightness variability of MWC 297 resembles the photometric activity of UX Ori type stars, which is due to variations of their circumstellar extinction, its scale is very far from the scales observed for UX Ori stars. It is difficult to reconcile the level of photometric activity with the idea that MWC 297 is observed through its own gas-dust disk viewed almost edge-on, as has been suggested in several studies.

ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

ABSTRACT We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 104.8 < L */L ☉ < 105.0 and the star was not extremely massive for a Type IIP progenitor, with M * < 15 M ☉. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with to 10−5.0 M ☉ yr−1 at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T * ≃ 3600+300 − 200 K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength (λ ⩾ 0.3 μm) and total (absorption plus scattering) V-band optical depth (τ V ⩽ 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.

Open clusters

Context. Spectroscopic investigations of galactic open clusters are scarce and limited to a reduced sample of cluster members.Aims. We intend to perform a complete study of the physical parameters of two galactic clusters as well as of their individual members.Methods. To carry out this study, we used the BCD (Barbier-Chalonge-Divan) spectrophotometric system, which is based on the study of the Balmer discontinuity and is independent of interstellar and circumstellar extinction. Additional physical properties were derived from the line profiles (FWHM) and stellar evolution models. We analyzed low-resolution spectra around the Balmer discontinuity for normal B-type and Be stars in two open clusters: NGC 3766 and NGC 4755. We determined the stellar fundamental parameters, such as effective temperatures, surface gravities, spectral types, luminosity classes, absolute and bolometric magnitudes, and color gradient excesses. The stellar rotation velocity was also determined. Complementary information, mainly stellar mass, age, and radius of the star population were calculated using stellar evolution models. In some cases, the stellar fundamental parameters were derived for the first time. The obtained results allowed us also to determine the reddening, age, and distance to the clusters.Results. The cluster parameters obtained through the BCD method agree very well with those derived from classical methods based on photometric data. The BCD system also provides physical properties of the star members. This study enables us to test the good behavior of M bol (λ 1 ,D )-calibrations and detect systematic discrepancies between log g estimates from model atmospheres and those derived from stellar evolution models. To improve our knowledge on the formation and evolution of the clusters, more statistical studies on the initial mass luminosity and angular momentum distributions should be addressed. Therefore, the BCD spectrophotometric system could be a powerful tool for studying far galactic and extragalactic clusters with the generation of large telescopes and the multi-object technique.

Photometric activity of UX Ori stars and related objects in the near infrared and visual. BF Ori, CQ Tau, WW Vul, and SV Cep

We have analyzed the activity of four UX Ori stars in the near-IR (JHKL) and visual (V) using the results of long-term photometric observations. For comparison, we also obtained IR (JHKLM) photometric observations of two visually quiet young stars of close spectral types (AB Aur and HD 190073). For the photometrically most active UX Ori stars BF Ori, CQ Tau, and WW Vul, the Algol-like declines of brightness in the visual, which are due to sporadic enhancements of the circumstellar extinction, are also observed (with decreasing amplitude) in the IR bands. A strict correlation between the V and J brightness variations is observed for all the stars except for SV Cep. For some of the UX Ori stars, a strong correlation between the visual and IR activity is observed up to L, where the main contribution to the emission is made by circumstellar dust. In the case of SV Cep, the visual variability is not correlated with the variability of the IR fluxes. On one occasion, a clear anti-correlation was even observed: a shallow, but prolonged decrease of the visual brightness was accompanied by an increase in the IR fluxes. This indicates that circumstellar clouds themselves can become powerful sources of IR emission. Our results provide evidence that the photometric activity of UX Ori stars is a consequence of instability of the deepest layers of their gas-dust accretion disks. In some cases (SV Cep), fluctuations of the density in this region are global, in the sense that they occur along a significant part of the circle marking the inner boundary of the dust disk. It is interesting that AB Aur, which is the quietest in the visual, appeared to be the most active in the IR. In contrast to UX Ori stars, the amplitude of its brightness variations increases from the J to the M band. It follows from analysis of the IR colors of this star that their variability cannot be described by models in which the variable IR emission has a temperature close to the sublimation temperature of silicate grains (about 1500 K). This means that the photometric activity of AB Aur must be due to both the dust and gas components of the circumstellar disk.

THE S 4 G PERSPECTIVE ON CIRCUMSTELLAR DUST EXTINCTION OF ASYMPTOTIC GIANT BRANCH STARS IN M100

We examine the effect of circumstellar dust extinction on the near-IR contribution of asymptotic giant branch (AGB) stars in intermediate-age clusters throughout the disk of M100. For our sample of 17 AGB-dominated clusters we extract optical-to-mid-IR SEDs and find that NIR brightness is coupled to the mid-IR dust emission in such a way that a significant reduction of AGB light, of up to 1 mag in K-band, follows from extinction by the dust shell formed during this stage. Since the dust optical depth varies with AGB chemistry (C-rich or O-rich), our results suggest that the contribution of AGB stars to the flux from their host clusters will be closely linked to the metallicity and the progenitor mass of the AGB star, to which dust chemistry and mass-loss rate are sensitive. Our sample of clusters--each the analogue of a ~1 Gyr old post-starburst galaxy--has implications within the context of mass and age estimation via SED modelling at high z: we find that the average ~0.5 mag extinction estimated here may be sufficient to reduce the AGB contribution in (rest-frame) K-band from ~70%, as predicted in the latest generation of synthesis models, to ~35%. Our technique for selecting AGB-dominated clusters in nearby galaxies promises to be effective for discriminating the uncertainties associated with AGB stars in intermediate-age populations that plague age and mass estimation in high-z galaxies.

The effects of dust on the optical and infrared evolution of SN 2004et

We present an analysis of multi-epoch observations of the Type II-P supernova SN 2004et. New and archival optical spectra of SN 2004et are used to study the evolution of the Halpha and [O I] 6300A line profiles between days 259 and 646. Mid-infrared imaging was carried out between 2004 to 2010. We include Spitzer `warm' mission photometry at 3.6 and 4.5um obtained on days 1779, 1931 and 2151, along with ground-based and HST optical and near-infrared observations obtained between days 79 and 1803. Multi-wavelength light curves are presented, as well as optical-infrared spectral energy distributions (SEDs) for multiple epochs. Starting from about day 300, the optical light curves provide evidence for an increasing amount of circumstellar extinction attributable to newly formed dust, with the additional extinction reaching 0.8-1.5 magnitudes in the V-band by day 690. The overall SEDs were fitted with multiple blackbody components, in order to investigate the luminosity evolution of the supernova, and then with Monte Carlo radiative transfer models using smooth or clumpy dust distributions, in order to estimate how much new dust condensed in the ejecta. The luminosity evolution was consistent with the decay of 56Co in the ejecta up until about day 690, after which an additional emission source is required, in agreement with the findings of Kotak et al. (2009). Clumped dust density distributions consisting of 20% amorphous carbons and 80% silicates by mass were able to match the observed optical and infrared SEDs, with dust masses that increased from 8x10^{-5} Msun on day 300 to 1.5x10^{-3} Msun on day 690, still significantly lower than the values needed for core collapse supernovae to make a significant contribution to the dust enrichment of galaxies.

Hydrodynamics of Young Binaries with Low-Mass Secondaries

AbstractThe model of a young star with a low-mass secondary component (q = M2/M1 ≤ 0.1) accreting matter from a circumbinary (CB) disc is considered. It is assumed that the orbit and the CB disc can be coplanar and non-coplanar. The model parameters were varied within the following ranges: the component mass ratio q ranged from 0.1 to 0.003, the eccentricity e varied from 0 to 0.7, the inclination of the orbit plane to the CB disc ranged from 0 to 10 degrees, and the parameter that defines the viscosity of the system was also varied. A number of hydrodynamics models of such a system have been calculated by the SPH method and then the variations of the circumstellar extinction and phase brightness curves were determined. The calculated brightness curves differ in shape and amplitude and it depends on the model parameters and the orientation of the system relative to the observer. The results were used to analyze the cyclic activity of UX Ori type stars.

The planetary nebulae population in the central regions of M32: the SAURON view

Extragalactic Planetary Nebulae (PNe) are not only useful as distance signposts or as tracers of the dark-matter content of their host galaxies, but constitute also good indicators of the main properties of their parent stellar populations. Yet, so far, the properties of PNe in the optical regions of galaxies where stellar population gradients can be more extreme have remained largely unexplored, mainly because the detection of PNe with narrow-band imaging or slit-less spectroscopy is considerably hampered by a strong stellar background. Integral-field spectroscopy (IFS) can overcome this limitation, and here we present a study of the PN population in the nearby compact elliptical M32. Using SAURON data taken with just two 10-minutes-long pointings we have doubled the number of known PNe within the effective radius of M32, detecting PNe five times fainter than previously found in narrow-band images that collected nearly the same number of photons. Furthermore, by carefully accounting for the incompleteness of our survey we could conclude, despite having only 15 sources, that the central PNe population of M32 is consistent with the generally adopted shape for the PNe Luminosity Function and its typical normalization observed in early-type galaxies. Finally, owing to the proximity of M32 and to UV images taken with HST, we could identify the most likely candidates for the central star of a subset of our detected PNe and conclude that these stars are affected by substantial amounts of circumstellar dust extinction, a finding that could reconcile the intriguing discrepancy previously reported in M32 between model predictions and observations for the later stages of stellar evolution. Considering the modest time investment on a 4m-class telescope that delivered these results, this work illustrates the potential of future IFS studies for the central PNe population of early-type galaxies.

Inner disc rearrangement revealed by dramatic brightness variations in the young star PV Cep

Young Sun-like stars at the beginning of the pre-main sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time scales and wavelength dependence of the variability carry information on the physical mechanisms behind these interactions. We conducted multi-epoch, multi-wavelength study of PV Cep, a strongly variable, accreting PMS star. By combining our own observations from 2004-2010 with archival and literature data, we show that PV Cep started a spectacular fading in 2005, reaching an I_C-band amplitude of 4 mag. Analysis of variation of the optical and infrared fluxes, colour indices, and emission line fluxes suggests that the photometric decline in 2005-2009 resulted from an interplay between variable accretion and circumstellar extinction: since the central luminosity of the system is dominated by accretion, a modest drop in the accretion rate could induce the drastic restructuring of the inner disc. Dust condensation in the inner disc region might have resulted in the enhancement of the circumstellar extinction.

Period-magnitude relation of Mira-like variables in the Large Magellanic Cloud as a tool to understanding circumstellar extinction

Near- to mid-infrared period-magnitude relations and also the period-bolometric luminosity relation of OGLE-III Mira-like variables in the LMC are derived. The relations have a kink, and the period at which the break occurs is quantitatively obtained. There are many Mira-like variables whose fluxes at the optical and the near-infrared wavebands are fainter than the ones predicted by the period-magnitude relations. The deviation is due to the circumstellar extinction, and the amount of the deviation is found to be strongly correlated with near-infrared colors. The empirical formulae relating the amount of the deviation and the near-infrared colors are derived. These relations are useful to accurately calculate the distances to the dusty Mira-like variables, because the dimmed fluxes due to the circumstellar extinction can be estimated. In a manner analogous to the interstellar extinction law, the ratios of deviations at any two different wavebands are calculated. The ratios are found to change with the pulsation period, indicating that the dust properties are subject to change as Mira-like variables evolve.

Modulation of circumstellar extinction in a young binary system with a low-mass companion in a noncoplanar orbit

We consider a model of cyclic brightness variations in a young star with a low-mass (q = M 2/M 1 ≤ 0.1) companion that accretes matter from the remnants of a protostellar cloud (circumbinary disk). We assume that the orbit of the companion is circular and that its plane does not coincide with the disk plane. We have computed grids of hydrodynamic models for such a binary by the SPH method based on which we have investigated the circumstellar extinction variations produced by the streams of matter and density waves excited in the circumbinary disk by the orbital motion of the companion. We show that, depending on the inclination and orientation of the binary’s line of nodes relative to the observer, the brightness of the primary component can undergo various (in shape and depth) oscillations with a period equal to the orbital one. In contrast to the models with coplanar circular orbits, the accretion rate onto the components of a binary with a noncoplanar orbit depends on the orbital phase. The results of our computations can be used to study the cyclic activity of UX Ori stars and young eclipsing binaries with anomalously long eclipses.

Spectroscopic study of the variable planetary nebula IC 4997

Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003–2009, we have obtained the relative fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time. The drop in the ratios F(λ4363)/F(Hγ) and F(λ363)/F(λ4959) that began back in 1990–1995 has continued, suggesting a decrease in the electron density and temperature in the central nebular region. The ratio F(λ6731)/F(λ6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N e ∼ 104 cm−3.

Spectral investigations of T Tauri stars

Basic ideas concerning the nature of young T Tauri stars (TTS) are briefly outlined and some examples of spectral investigations of those stars are considered. The photometric and spectral variability of TTS is believed to be due to circumstellar extinction, magnetic activity, and accretion of matter from the circumstellar disk onto the stellar surface. In the 1990s, a series of high resolution spectra of several TTS were obtained using the SOFIN echelle spectrograph with the Nordic Optical Telescope (NOT). In particular, the emission lines in the spectra of the star RW Aur A were shown to be rotationally modulated with a period of 2.7 days, which was interpreted in terms of the magnetospheric accretion model with an inclined magnetic rotator. The spectra of TTS obtained using the UVES spectrograph with the VLT demonstrated that the effect of veiling the photospheric spectrum, usually attributed to accretion, was largely due to chromospheric extinction. The accretion is suggested to be a complementary heating source in chromospheres of TTS.

The destruction and survival of dust in the shell around SN 2008S

SN 2008S erupted in early 2008 in the grand design spiral galaxy NGC 6946. The progenitor was detected by Prieto et al. in Spitzer Space Telescope images taken over the four years prior to the explosion, but was not detected in deep optical images, from which they inferred a self-obscured object with a mass of about 10 Msun. We obtained Spitzer observations of SN 2008S five days after its discovery, as well as coordinated Gemini and Spitzer optical and infrared observations six months after its outburst. We have constructed radiative transfer dust models for the object before and after the outburst, using the same r^-2 density distribution of pre-existing amorphous carbon grains for all epochs and taking light-travel time effects into account for the early post-outburst epoch. We rule out silicate grains as a significant component of the dust around SN 2008S. The inner radius of the dust shell moved outwards from its pre-outburst value of 85 AU to a post-outburst value of 1250 AU, attributable to grain vaporisation by the light flash from SN 2008S. Although this caused the circumstellar extinction to decrease from Av = 15 before the outburst to 0.8 after the outburst, we estimate that less than 2% of the overall circumstellar dust mass was destroyed. The total mass-loss rate from the progenitor star is estimated to have been (0.5-1.0)x10^-4 Msun yr^-1. The derived dust mass-loss rate of 5x10^-7 Msun yr^-1 implies a total dust injection into the ISM of up to 0.01 Msun over the suggested duration of the self-obscured phase. We consider the potential contribution of objects like SN 2008S to the dust enrichment of galaxies.

PLANETARY NEBULAE IN FACE-ON SPIRAL GALAXIES. II. PLANETARY NEBULA SPECTROSCOPY

As the second step in our investigation of the mass-to-light ratio of spiral disks, we present the results of a spectroscopic survey of planetary nebulae (PNe) in five nearby, low-inclination galaxies: IC 342, M74 (NGC 628), M83 (NGC 5236), M94 (NGC 4736), and M101 (NGC 5457). Using 50 setups of the WIYN/Hydra and Blanco/Hydra spectrographs, and 25 observations with the Hobby-Eberly Telescope's Medium Resolution Spectrograph, we determine the radial velocities of 99, 102, 162, 127, and 48 PNe, respectively, to a precision better than 15 km/s. Although the main purpose of this data set is to facilitate dynamical mass measurements throughout the inner and outer disks of large spiral galaxies, our spectroscopy has other uses as well. Here, we co-add these spectra to show that to first order, the [O III] and Balmer line ratios of planetary nebulae vary little over the top ~1.5 mag of the planetary nebula luminosity function. The only obvious spectral change occurs with [N II], which increases in strength as one proceeds down the luminosity function. We also show that typical [O III]-bright planetaries have E(B-V) ~ 0.2 of circumstellar extinction, and that this value is virtually independent of [O III] luminosity. We discuss the implications this has for understanding the population of PN progenitors.

Long-term photometry and periods for 261 nearby pulsating M giants

We present the results of a 5.5-year CCD photometric campaign that monitored 261 bright, southern, semi-regular variables with relatively precise Hipparcos parallaxes. The data are supplemented with independent photoelectric observations of 34 of the brightest stars, including 11 that were not part of the CCD survey, and a previously unpublished long time-series of VZ Cam. Pulsation periods and amplitudes are established for 247 of these stars, the majority of which have not been determined before. All M giants with sufficient observations for period determination are found to be variable, with 87% of the sample (at S/N >= 7.5) exhibiting multi-periodic behaviour. The period ratios of local SRVs are in excellent agreement with those in the Large Magellanic Cloud. Apparent K-band magnitudes are extracted from multiple NIR catalogues and analysed to determine the most reliable values. We review the effects of interstellar and circumstellar extinction and calculate absolute K-band magnitudes using revised Hipparcos parallaxes.

Variability of the transitional T Tauri star T Chamaeleontis

We characterize the physical properties of T Chamaeleontis, a transitional T Tauri star showing UX Ori-type variability, and of its associated disc, and probe possible effects of disc clearing processes. Different spectral diagnostics are examined, based on a rich collection of optical high- and low-resolution spectra. We determine radial and projected rotational velocities, and measure equivalent widths of the Li I (6708 A) line and of the most prominent emission lines (e.g. Ha, Hb and [OI] 6300A); we analyse shape changes of photospheric lines via bisector-method, while variability in Ha and Hb is inspected through line-profile correlation matrices. The strength of the Ha and Hb emission is highly variable and well correlated with that of the [OI] lines, as well as with Av variations of over three magnitudes. Variations up to nearly 10 km/s in the radial velocity of the star are measured on analogous time-scale, but with no apparent periodicity. SED modelling confirms the existence of a gap in the disc. Variable circumstellar extinction is pointed out as responsible for the conspicuous variations observed in the stellar continuum flux and for concomitant changes in the emission features by contrast effect. Clumpy structures, incorporating large dust grains and orbiting the star within a few tenths of AU, obscure episodically the star and, eventually, part of the inner circumstellar zone, while the bulk of the hydrogen lines emitting zone and outer low-density wind region traced by the [OI] remain unaffected. Coherently with this scenario, the detected radial velocity changes are also explainable in terms of clumpy materials transiting and partially obscuring the star.

Parameters of galactic early B supergiants

Context. The interstellar extinction, E(B - V), of OB supergiants is usually derived from the observed color index, (B - V), in comparison with the intrinsic one. This method works properly only if the stellar wind does not influence the optical continuum emission. Over the past years, many OB supergiants have been found to have wind-velocity distributions with rather high β values; i.e., their winds are only slowly accelerating, resulting in relative density enhancements within the wind-continuum forming region. It has been found that these kinds of winds might indeed influence the total continuum emission even at optical wavelengths. Aims. We investigate the influence of the wind on the observed color indices of OB supergiants, in order to distinguish between interstellar and circumstellar extinction contributions. Methods. We first tested the influence of the wind on the UBV band fluxes of a model O supergiant star with artificial winds of different β values and a fixed interstellar extinction value. From the UBV magnitudes of these systems, the apparent interstellar extinction was then derived by calculating the values of E(B - V), from the (B - V) as well as from the (U - B) color index. Then we turned to a sample of galactic early-type B supergiants for which the stellar and wind parameters are known. All except one of these stars have β values higher than 1.0, which makes this set the most suitable one for our investigation. We calculated each star's wind contribution to the BV band fluxes. The observed magnitudes were corrected for the wind contributions, and the interstellar extinctions were derived and compared with those derived purely from the (B - V) color index. Results. From our model supergiant, we find that with increasing β the wind starts to influence the observable color indices. The wavelength dependence of the wind contribution is thereby different from that of the interstellar extinction contribution. Thus, the interstellar extinction values derived from the two color indices of our reddened star plus wind systems disagree. This effect is stronger for higher β. In addition, E(B ― V) derived from the (B ― V) color index always overestimates the real interstellar extinction. This trend is also found for the investigated B supergiant sample. Consequently, the luminosities of these stars are systematically overestimated. Our wind model always computes lower limits to the real wind contributions. This means that the real interstellar extinction values, hence the stellar luminosities of the studied B supergiant sample, might well be lower.

Photometric activity of the UX Ori star V1184 Tau in the optical and near-infrared spectral ranges

We present the results of our infrared JHK photometry for the unusual UX Ori star V1184 Tau. Comparison with previous observations performed before the catastrophic decline in its optical brightness in 2004 (when the star faded approximately by a factor of 100) has shown the following: the star faded approximately by 2m and 1m in the J and H bands, respectively, while its K brightness remained almost constant. This pattern of infrared variability seems incompatible with the mechanism of variable circumstellar extinction responsible for the dramatic decline in the star’s optical brightness. However, if this mechanism is considered in the context of an accretion disk model with a puffed-up inner rim in the dust sublimation zone and with a disk wind producing an expanding gas-dust atmosphere above the disk surface, then the paradox can be resolved. In this model, the photometric activity of V1184 Tau in both visible and near-infrared spectral ranges, including the sharp brightness decline in 2004, can be explained by an increase in the geometric thickness of the disk in the dust sublimation zone caused by enhanced accretion of circumstellar matter onto the star. There is reason to believe that such events occur periodically and result from the presence of a companion to V1184 Tau moving in a highly eccentric orbit. The offered interpretation of the photometric activity of V1184 Tau allows this object to be classified as an UX Ori star based on the observed photometric effect and, at the same time, as a FU Ori star based on the pattern of the physical process that produced this effect.

Deep near-IR variability survey of pre-main-sequence stars in ρ Ophiuchi

Context. Variability is a common characteristic of pre-main-sequence stars (PMS). Near-IR variability surveys of young stellar objects (YSOs) can probe stellar and circumstellar environments and provide information about the dynamics of the ongoing magnetic and accretion processes. Furthermore, variability can be used as a tool to uncover new cluster members in star formation regions. Aims. We hope to achieve the deepest near-IR variability study of YSOs targeting the ρ Ophiuchi cluster. Methods. Fourteen epochs of observations were obtained with the Wide Field Camera (WFCAM) at the UKIRT telescope scheduled in a manner that allowed the study of variability on timescales of days, months, and years. Statistical tools, such as the multi-band cross correlation index and the reduced chi-square, were used to disentangle signals of variability from noise. Variability characteristics are compared to existing models of YSOs in order to relate them to physical processes, and then used to select new candidate members of this star-forming region. Results. Variability in the near-IR is found to be present in 41% of the known population of ρ Ophiuchi recovered in our sample. The behaviours shown are several and can be associated with the existence of spots on the stellar surface, variations in circumstellar extinction, or changes in the geometry of an accretion disc. Using variability, a new population of objects has been uncovered that is believed to be part of the ρ Ophiuchi cluster.