arXiv subjects

Belinda Damian

Publications and source records attributed to Belinda Damian.

13 recordsLinked to original sources

arXiv2026

Revealing the substellar population of IC 1396: A spectroscopic survey of brown dwarfs in the region

We present a new spectroscopic view of the brown dwarf population in the young star-forming region IC 1396 and investigate the impact of environment on low-mass star formation. We use deep optical photometry from Subaru-HSC to identify the candidate low-mass stars and brown dwarfs in the region. Our follow-up low-resolution spectroscopic survey with GTC-EMIR and IRTF-SpeX has identified 32 new members in the region with spectral types between M3 and M9, among which 25 are brown dwarfs with spectral types M6 or later. We use the BT-Settl atmospheric models to derive the effective temperatures of the members. Using a comprehensive catalogue of known members and candidates, we estimate the star to brown dwarf ratio for IC 1396 to be 5.0$\pm$0.4, for a mass range between 1-0.03 M$_\odot$. This ratio is largely consistent with measurements in other young clusters spanning a range of UV radiation fields and stellar densities, supporting formation scenarios in which the relative abundance of brown dwarfs is not strongly influenced by the local environmental conditions.

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arXiv2025

The substellar population in Corona Australis

The substellar initial mass function (IMF) and the formation mechanisms of brown dwarfs (BDs) remain key open questions in star formation theory. IMF characterization in a large number of star-forming regions (SFRs) is essential for constraining these processes. We aim to identify and spectroscopically confirm very low-mass members of the Corona Australis (CrA) SFR to refine its substellar census, determine its low-mass IMF, and compare it to other clusters. Using deep I-band photometry from SuprimeCam/Subaru and data from the VISTA Hemisphere Survey, we identified low-mass BD candidates in CrA. We subsequently obtained NIR spectra of 173 of these candidates with KMOS/VLT, as well as optical spectra for 8 kinematic candidate members using FLOYDS/LCO. The kinematic candidates are confirmed as low-mass stellar members with spectral types M1 to M5. In contrast, all 173 BD candidates observed with KMOS are identified as contaminants. Although the follow-up yielded no new substellar members, it places strong constraints on the number of undetected substellar objects in the region. Combined with literature data, this enables us to derive the substellar IMF, which is consistent with a single power-law slope of alpha = 0.95+-0.06 in the range 0.01-1 MSun or alpha = 0.33+-0.19 in the range 0.01-0.1 MSun. The star-to-BD ratio in CrA is about 2. We also provide updated IMFs and star-to-BD ratios for Lupus3 and ChaI from the SONYC survey, reflecting revised distances from Gaia. Finally, we estimate surface densities and median FUV fluxes for 6 SFRs and clusters and compare their substellar populations as a function of environmental properties. The IMF and star-to-BD ratio show no clear dependence on stellar density or ionizing flux from the massive stars. A combined effect - where one factor enhances and the other suppresses BD formation - also appears unlikely. (Abridged)

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arXiv2025

Spectroscopy of Free-Floating Planetary-Mass Objects and their disks with JWST

Free-floating planetary-mass objects (FFPMOs) are known to harbor disks at young ages. Here, we present 1-13 $μm$ spectra for eight young FFPMOs with masses of 5-10 M$_\mathrm{Jup}$ (at ages of 1-5 Myr), using the NIRSpec and MIRI instruments on the James Webb Space Telescope. We derive fundamental properties of these targets, and find spectral types of M9.5 to L4, with effective temperatures of 1600-1900 K. The photospheric spectra of our targets show a clear diversity at similar temperatures, especially in the 3-5 $μm$ range, unaccounted for by existing atmospheric models. We find a silicate absorption feature in the photosphere of one of our targets, the first such detection in very young FFPMOs, indicating silicate clouds in their cool atmospheres. Six of our objects show mid-infrared excess emission above the photosphere, as well as silicate emission features, demonstrating the presence of disks. The shape and strength of the latter features constitute strong evidence of grain growth and crystallization, similar to what is seen in more massive brown dwarfs and stars. We also detect emission lines from hydrocarbon molecules in the disks of several targets. These are the lowest mass isolated objects found so far with silicate and hydrocarbon emission features arising in their disks. The presence of disks and their characteristics point to the potential for the formation of rocky companions around free-floating planetary-mass objects.

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arXiv2025

Detection of Hydrocarbons in the Disk around an Actively-Accreting Planetary-Mass Object

We present the 0.6--12-micron spectrum of Cha\,1107-7626, a 6-10 Jupiter-mass free-floating object in the $\sim$2\,Myr-old Chamaeleon-I star-forming region, from observations with the NIRSpec and MIRI instruments onboard the James Webb Space Telescope. We confirm that Cha\,1107-7626 is one of the lowest-mass objects known to harbor a dusty disk with infrared excess emission at wavelengths beyond 4 microns. Our NIRSpec data, and prior ground-based observations, provide strong evidence for ongoing accretion through Hydrogen recombination lines. In the mid-infrared spectrum, we detect unambiguously emission lines caused by methane (CH$_\mathrm{4}$) and ethylene (C$_\mathrm{2}$H$_\mathrm{4}$) in its circum-substellar disk. Our findings mean that Cha 1107-7626 is by far the lowest-mass object with hydrocarbons observed in its disk. The spectrum of the disk looks remarkably similar to that of ISO-ChaI 147, a very low mass star with a carbon-rich disk that is 10 to 20 times more massive than Cha\,1107-7626. The hydrocarbon lines can be accounted for with a model assuming gas temperatures of a few hundred Kelvin in the inner disk. The obvious similarities between the spectra of a low-mass star and a planetary-mass object indicate that the conditions in the inner disks can be similar across a wide range of central object masses.

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arXiv2024

A Novel Survey for Young Substellar Objects with the W-band Filter. VII. Water-Bearing Objects in the Core of the Rho Ophiuchi Cloud Complex

We present a study of very low-mass stars and brown dwarfs in the rich star-forming core of the Rho Ophiuchi cloud complex. The selection of the sample relies on detecting the inherent water absorption characteristic in young substellar objects. Of the 22 water-bearing candidates selected, 15 have a spectral type of M6 or later. Brown dwarf candidates too faint for membership determination by Gaia have their proper motions derived by deep-infrared images spanning six years. Astrometric analysis confirms 21/22 sources as members, one identified as a contaminant. Infrared colors and the spectral energy distribution of each water-bearing candidate are used to diagnose the mass, age, and possible existence of circumstellar dust. 15 sources exhibit evidence of disks in their spectral energy distributions, as late as in M8-type objects. Spectroscopy for bright candidates has confirmed one as an M8 member and verified two sources (with disks) exhibiting signatures of magnetospheric accretion.

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arXiv2024

Twins in Diversity: Understanding circumstellar disk evolution in the twin clusters of W5 complex

Young star-forming regions in massive environments are ideal test beds to study the influence of surroundings on the evolution of disks around low-mass stars. We explore two distant young clusters, IC 1848-East and West located in the massive W5 complex. These clusters are unique due to their similar (distance, age, and extinction) yet distinct (stellar density and FUV radiation fields) physical properties. We use deep multi-band photometry in optical, near-IR, and mid-IR wavelengths complete down to the substellar limit in at least five bands. We trace the spectral energy distribution of the sources to identify the young pre-main sequence members in the region and derive their physical parameters. The disk fraction for the East and West clusters down to 0.1 M$_\odot$ was found to be $\sim$27$\pm$2% (N$_{disk}$=184, N$_{diskless}$=492) and $\sim$17$\pm$1% (N$_{disk}$=173, N$_{diskless}$=814), respectively. While no spatial variation in the disk fraction is observed, these values are lower than those in other nearby young clusters. Investigating the cause of this decrease, we find a correlation with the intense feedback from massive stars throughout the cluster area. We also identified the disk sources undergoing accretion and observed the mass accretion rates to exhibit a positive linear relationship with the stellar host mass and an inverse relationship with stellar age. Our findings suggest that the environment significantly influences the dissipation of disks in both clusters. These distant clusters, characterized by their unique attributes, can serve as templates for future studies in outer galaxy regions, offering insights into the influence of feedback mechanisms on star and planetary formation.

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arXiv2024

Search for Brown Dwarfs in IC 1396 with Subaru HSC: Interpreting the Impact of Environmental Factors on Sub-stellar Population

Young stellar clusters are predominantly the hub of star formation and hence, ideal to perform comprehensive studies over the least explored sub-stellar regime. Various unanswered questions like the mass distribution in brown dwarf regime and the effect of diverse cluster environment on brown dwarf formation efficiency still plague the scientific community. The nearby young cluster, IC 1396 with its feedback-driven environment, is ideal to conduct such study. In this paper we adopt a multi-wavelength approach, using deep Subaru HSC, Gaia DR3, Pan-STARRS, UKIDSS/2MASS photometry and machine learning techniques to identify the cluster members complete down to $\sim$ 0.03 M$_{\odot}$ in the central 22$^{\prime}$ area of IC 1396. We identify 458 cluster members including 62 brown dwarfs which are used to determine mass distribution in the region. We obtain a star-to-brown dwarf ratio of $\sim$ 6 for a stellar mass range 0.03 -- 1 M$_{\odot}$ in the studied cluster. The brown dwarf fraction is observed to increase across the cluster as radial distance from the central OB-stars increases. This study also compiles 15 young stellar clusters to check the variation of star-to-brown dwarf ratio relative to stellar density and UV flux ranging within 4-2500 stars pc$^{-2}$ and 0.7-7.3 G$_{0}$ respectively. The brown dwarf fraction is observed to increase with stellar density but the results about the influence of incident UV flux are inconclusive within this range. This is the deepest study of IC 1396 as of yet and it will pave the way to understand various aspects of brown dwarfs using spectroscopic observations in future.

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arXiv2023

Protoplanetary disks around young stellar and substellar objects in the $σ$ Orionis cluster

Understanding the evolution and dissipation of protoplanetary disks are crucial in star and planet formation studies. We report the protoplanetary disk population in the nearby young $σ$ Orionis cluster (d$\sim$408 pc; age$\sim$1.8 Myr) and analyse the disk properties such as dependence on stellar mass and disk evolution. We utilise the comprehensive census of 170 spectroscopic members of the region refined using astrometry from Gaia DR3 for a wide mass range of $\sim$19-0.004 M$_\odot$. Using the near infrared (2MASS) and mid infrared (WISE) photometry we classify the sources based on the spectral index into class I, class II, flat spectrum and class III young stellar objects. The frequency of sources hosting a disk with stellar mass $<$2 M$_\odot$ in this region is 41$\pm$7% which is consistent with the disk fraction estimated in previous studies. We see that there is no significant dependence of disk fraction on stellar mass among T Tauri stars ($<$2 M$_\odot$), but we propose rapid disk depletion around higher mass stars ($>$2 M$_\odot$). Furthermore we find the lowest mass of a disk bearing object to be $\sim$ 20 M$_\mathrm{Jup}$ and the pronounced disk fraction among the brown dwarf population hints at the formation scenario that brown dwarfs form similar to low-mass stars.

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arXiv2023

A novel survey for young substellar objects with the W-band filter VI: Spectroscopic census of sub-stellar members and the IMF of $σ$ Orionis cluster

Low-mass stars and sub-stellar objects are essential in tracing the initial mass function (IMF). We study the nearby young $σ$ Orionis cluster (d$\sim$408 pc; age$\sim$1.8 Myr) using deep NIR photometric data in J, W and H-bands from WIRCam on the Canada-France-Hawaii Telescope. We use the water absorption feature to photometrically select the brown dwarfs and confirm their nature spectroscopically with the IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and that of literature sources using astrometry from Gaia DR3. We obtain the near-IR spectra for 28 very low-mass stars and brown dwarfs and estimate their spectral type between M3-M8.5 (mass ranging between 0.3-0.01 M$_{\odot}$). Apart from these, we also identify 5 new planetary mass candidates which require further spectroscopic confirmation of youth. We compile the comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of $\sim$19-0.004 M$_{\odot}$. We estimate the star/BD ratio to be $\sim$4, within the range reported for other nearby star forming regions. With the updated catalog of members we trace the IMF down to 4 M$_\mathrm{Jup}$ and we find that a two-segment power-law fits the sub-stellar IMF better than the log-normal distribution.

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arXiv2022

A Novel Survey for Young Substellar Objects with the W band Filter.V. IC 348 and Barnard 5 in the Perseus Cloud

We report the discovery of substellar objects in the young star cluster IC 348 and the neighboring Barnard 5 dark cloud, both at the eastern end of the Perseus star-forming complex. The substellar candidates are selected using narrowband imaging, i.e., on and off photometric technique with a filter centered around the water absorption feature at 1.45 microns, a technique proven to be efficient in detecting water-bearing substellar objects. Our spectroscopic observations confirm three brown dwarfs in IC 348. In addition, the source WBIS 03492858+3258064, reported in this work, is the first confirmed brown dwarf discovered toward Barnard 5. Together with the young stellar population selected via near- and mid-infrared colors using the Two Micron All Sky Survey and the Wide-field Infrared Survey Explorer, we diagnose the relation between stellar versus substellar objects with the associated molecular clouds. Analyzed by Gaia EDR3 parallaxes and kinematics of the cloud members across the Perseus region, we propose the star formation scenario of the complex under influence of the nearby OB association.

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arXiv2021

Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex -- I: Introduction, Photometry and Source Catalog

Low mass star formation inside massive clusters is crucial to understand the effect of cluster environment on processes like circumstellar disk evolution, planet and brown dwarf formation. The young massive association of Cygnus OB2, with a strong feedback from massive stars, is an ideal target to study the effect of extreme environmental conditions on its extensive low-mass population. We aim to perform deep multi-wavelength studies to understand the role of stellar feedback on the IMF, brown dwarf fraction and circumstellar disk properties in the region. We introduce here, the deepest and widest optical photometry of 1.5$^\circ$ diameter region centred at Cygnus OB2 in r$_{2}$, i$_{2}$, z and Y-filters using Subaru Hyper Suprime-Cam (HSC). This work presents the data reduction, source catalog generation, data quality checks and preliminary results about the pre-main sequence sources. We obtain 713,529 sources in total, with detection down to $\sim$ 28 mag, 27 mag, 25.5 mag and 24.5 mag in r$_{2}$, i$_{2}$, z and Y-band respectively, which is $\sim$ 3 - 5 mag deeper than the existing Pan-STARRS and GTC/OSIRIS photometry. We confirm the presence of a distinct pre-main sequence branch by statistical field subtraction of the central 18$^\prime$ region. We find the median age of the region as $\sim$ 5 $\pm$ 2 Myrs with an average disk fraction of $\sim$ 9$\%$. At this age, combined with A$_V$ $\sim$ 6 - 8 mag, we detect sources down to a mass range $\sim$ 0.01 - 0.17 M$_\odot$. The deep HSC catalog will serve as the groundwork for further studies on this prominent active young cluster.

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arXiv2021

A Novel Survey for Young Substellar Objects with the W-band filter III: Searching for very low mass brown dwarfs in Serpens South and Serpens Core

We present CFHT photometry and IRTF spectroscopy of low-mass candidate members of Serpens South and Serpens Core ($\sim$430 pc, $\sim$0.5 Myr), identified using a novel combination of photometric filters, known as the W-band method. We report SC182952+011618, SS182959-020335 and SS183032-021028 as young, low-mass Serpens candidate members, with spectral types in the range M7-M8, M5-L0 and M5-M6.5 respectively. Best-fit effective temperatures and luminosities imply masses of $<$ 0.12M$_{\odot}$ for all three candidate cluster members. We also present Hubble Space Telescope imaging data (F127M, F139M and F850LP) for six targets in Serpens South. We report the discovery of the binary system SS183044-020918AB. The binary components are separated by $\approx$45 AU, with spectral types of M7-M8 and M8-M9, and masses of 0.08-0.1 and 0.05-0.07M$_{\odot}$. We discuss the effects of high dust attenuation on the reliability of our analysis, as well as the presence of reddened background stars in our photometric sample.

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arXiv2021

Testing the role of environmental effects on the initial mass function of low-mass stars

In the star formation process, the vital impact of environmental factors such as feedback from massive stars and stellar density on the form of the initial mass function (IMF) at low-mass end is yet to be understood. Hence a systematic, highly sensitive observational analysis of a sample of regions under diverse environmental conditions is essential. We analyse the IMF of eight young clusters ($<$5 Myr), namely IC1848-West, IC1848-East, NGC 1893, NGC 2244, NGC 2362, NGC 6611, Stock 8 and Cygnus OB2, which are located at the Galactocentric distance ($R_g$) range $\sim$6-12 kpc along with nearby cluster IC348 using deep near-IR photometry and Gaia DR2. These clusters are embedded in massive stellar environments of radiation strength $log(L_{FUV}/L_{\odot})$ $\sim$2.6 to 6.8, $log(L_{EUV})$ $\sim$42.2 to 50.85 photons/s, with stellar density in the range of $\sim$170 - 1220 stars/pc$^2$. After structural analysis and field decontamination we obtain an unbiased, uniformly sensitive sample of pre-main-sequence members of the clusters down to brown-dwarf regime. The lognormal fit to the IMF of nine clusters gives the mean characteristic mass ($m_c$) and $σ$ of 0.32$\pm$0.02 $M_\odot$ and 0.47$\pm$0.02, respectively. We compare the IMF with that of low- and high-mass clusters across the Milky Way. We also check for any systematic variation with respect to the radiation field strength, stellar density as well with $R_g$. We conclude that there is no strong evidence for environmental effect in the underlying form of the IMF of these clusters.

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