arXiv subjects

D. K. Ojha

Publications and source records attributed to D. K. Ojha.

At least 145 records · Page 8Linked to original sources

arXiv2006

A multiwavelength study of the massive star forming region IRAS 06055+2039 (RAFGL 5179)

We present a multiwavelength study of the massive star forming region associated with IRAS 06055+2039 which reveals an interesting scenario of this complex where regions are at different stages of evolution of star formation. Narrow band near-infrared (NIR) observations were carried out with UKIRT-UFTI in molecular hydrogen and Br$γ$ lines to trace the shocked and ionized gases respectively. We have used 2MASS $J H K_{s}$ data to study the nature of the embedded cluster associated with IRAS 06055+2039. We obtain a power-law slope of 0.43$\pm$0.09 for the $K_{s}$-band Luminosity Function (KLF) which is in good agreement with other young embedded clusters. We estimate an age of 2 -- 3 Myr for this cluster. The radio emission from the ionized gas has been mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India. Apart from the diffuse emission, the high resolution 1280 MHz map also shows the presence of several discrete sources which possibly represent high density clumps. The morphology of shocked molecular hydrogen forms an arc towards the N-E of the central IRAS point source and envelopes the radio emission. Submillimetre emission using JCMT-SCUBA show the presence of a dense cloud core which is probably at an earlier evolutionary stage compared to the ionized region with shocked molecular gas lying in between the two. Emission from warm dust and the Unidentified Infrared Bands (UIBs) have been estimated using the mid-infrared (8 -- 21 $μ$m) data from the MSX survey. From the submillimetre emission at 450 and 850 $μ$m the total mass of the cloud is estimated to be $\sim$ 7000 -- 9000 $\rm M_{\odot}$.

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arXiv2005

Post-outburst radio observation of the region around McNeil's nebula (V1647 Ori)

We present post-outburst (~ 100 days after outburst) radio continuum observation of the region (~ 30' x 30') around McNeil's nebula (V1647 Orionis). The observations were carried out using the Giant Metrewave Radio Telescope (GMRT), India, at 1272 MHz on 2004 Feb 14.5 UT. Although 8 sources have been detected within a circular diameter of 25' centred on V1647 Ori, we did not detect any radio continuum emission from McNeil's nebula. We assign a 5-sigma upper limit of 0.15 mJy/beam for V1647 Ori where the beam size is 5.6" x 2.7". Even at higher frequencies of 4.9 and 8.5 GHz (VLA archival data), no radio emission has been detected from this region. Three scenarios namely, emission from homogeneous HII region, ionised stellar wind and shock ionised gas, are explored in the light of our GMRT upper-limit. For the case of homogeneous HII region, the radius of the emitting region is constrained to be <~ 26 AU corresponding to a temperature >~ 2,500 K, which is consistent with the reported radio and H-alpha emission. In the ionised stellar wind picture, our upper limit of radio emission translates to the ratio of mass loss rate and terminal velocity, (M_dot/v_infinity) < 1.2-1.8 x 10^(-10) (M_sun/yr)/(km/s). On the other hand, if the stellar wind shocks the dense neutral (molecular) cloud, the radio upper limit implies that the fraction of the wind encountering the dense obstacle is <50%. Based on a recent measurement of X-ray outburst and later monitoring, the expected radio emission has been estimated. Using our radio limit, the radius (<~ 36 AU) and electron density (>~ 7.2 x 10^7 cm^(-3) of the radio emitting plasma have been constrained using a two phase medium in pressure equilibrium for a volume filling factor of 0.9.

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arXiv2005

Infrared and radio study of star forming regions associated with IRAS 19111+1048 and IRAS 19110+1045

A multiwavelength study of the star forming regions associated with IRAS 19111+1048 and IRAS 19110+1045 has been carried out. These have been simultaneously mapped in two far infrared bands at lambda_eff ~ 130 and 200 micron with ~1' angular resolution using the TIFR 1-m balloon borne telescope. The radio emission from the ionised gas of these regions has been imaged at 1280, 610 and 325 MHz using the Giant Metrewave Radio Telescope, India. A total of 20 compact radio sources have been detected from the high resolution radio map of IRAS 19111+1048 at 1280 MHz. Assuming these sources to represent exciting zero age main sequence (ZAMS) stars, the initial mass function is found to be quite steep, with the power law index of 5.3+-0.5 for the mass range 14 < m/M_sun < 33. The spectral types of the ZAMS stars inferred independently from the radio and NIR measurements match very well for a good fraction of the radio sources having NIR counterparts. For IRAS 19110+1045 region, seven radio sources have been detected of which two are associated with deeply embedded 2MASS objects. Self consistent radiative transfer modelling aimed at extracting important physical and geometrical details of the two IRAS sources has been carried out. A uniform density distribution of dust and gas is implied for both the sources. The extents of ionised gas, number of ZAMS stars, presence of deeply embedded sources and lower value of L/M for the cloud, support the youth of IRAS 19110+1045 vis-a-vis its neighbour, IRAS 19111+1048, consistent with earlier studies.

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arXiv2005

Warp signatures of the Galactic disk as seen in mid infrared from Midcourse Space Experiment

The gross features in the distribution of stars as well as warm (T >~ 100 K) interstellar dust in the Galactic disk have been investigated using the recent mid infrared survey by Midcourse Space Experiment (MSX) at 8, 12, 14 & 21 micron bands. An attempt has been made to determine the location of the Galactic mid-plane at various longitudes, using two approaches : (i) fitting exponential functions to the latitude profiles and (ii) statistical indicators.The former method is successful for the inner Galaxy (-90 < l < 90), and quantifies characteristic angular scales along latitude, which have been translated to linear scale heights (z_h) and radial length scales (R_l) using geometric description of the Galactic disk. The distribution of warm dust in the Galactic disk is found to be characterised by R_l < 6 kpc and 60 < z_h <~ 100 pc, in agreement with other studies. The location of the Galactic mid-plane as a function of longitude, for stars as well as warm dust, has been searched for signatures of warp-like feature in their distribution, by fitting sinusoid with phase and amplitude as parameters. In every case, the warp signature has been detected. An identical analysis of the DIRBE/COBE data in all its ten bands covering the entire infrared spectrum (1.25-240 micron), also leads to detection of warp signatures with very similar phase as found from the MSX data. Our results have been compared with those from other studies.

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arXiv2004

V1647 Orionis (IRAS 05436-0007) : A New Look at McNeil's Nebula

We present a study of the newly discovered McNeil's nebula in Orion using the JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen extending toward north and south from the NIR source (V1647 Orionis) that illuminates McNeil's nebula. The compact nebula has an apparent diameter of about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure with two rims extending toward north-east and north-west. The north-east rim is brighter and sharp, while the north-west rim is diffuse. The north-east rim can be traced out to ~ 40 arcsec from the location of the NIR source. In contrast, no cavity structure is seen toward the south, although diffuse nebula is extended out to ~ 20 arcsec. New NIR photometric data show a significant variation in the magnitudes (> 0.15 mag) of the source of McNeil's nebula within a period of one week, that is possibly under the phase of eruptive variables like FUors or EXors.

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arXiv2004

A near-infrared study of the NGC 7538 star forming region

We present sub-arcsecond (FWHM ~ 0".7), NIR JHKs-band images and a high sensitivity radio continuum image at 1280 MHz, using SIRIUS on UH 88-inch telescope and GMRT. The NIR survey covers an area of ~ 24 arcmin^2 with 10-sigma limiting mags of ~ 19.5, 18.4, and 17.3 in J, H, and Ks-band, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of NGC 7538 star forming region. We construct JHK CC and J-H/J and H-K/K CM diagrams to identify YSOs and to estimate their masses. Based on these CC and CM diagrams, we identified a rich population of YSOs (Class I and Class II), associated with the NGC 7538 region. A large number of red sources (H-K > 2) have also been detected around NGC 7538. We argue that these red stars are most probably PMS stars with intrinsic color excesses. Most of YSOs in NGC 7538 are arranged from the N-W toward S-E regions, forming a sequence in age: the diffuse H II region (N-W, oldest: where most of the Class II and Class I sources are detected); the compact IR core (center); and the regions with the extensive IR reflection nebula and a cluster of red young stars (S-E and S). We find that the slope of the KLF of NGC 7538 is lower than the typical values reported for the young embedded clusters, although equally low values have also been reported in the W3 Main star forming region. From the slope of the KLF and the analysis by Megeath et al. (1996), we infer that the embedded stellar population is comprised of YSOs with an age of ~ 1 Myr. Based on the comparison between models of PMS stars with the observed CM diagram we find that the stellar population in NGC 7538 is primarily composed of low mass PMS stars similar to those observed in the W3 Main star forming region.

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arXiv2004

Deep near-infrared observations of W3 Main star forming region

We present a deep JHKs-band imaging survey of the W3 Main star forming region, using the near-infrared camera, SIRIUS, mounted on the University of Hawaii 2.2m telescope. The near-infrared survey covers an area of ~ 24 sq. arcmin with 10 sigma limiting magnitudes of ~ 19.0, 18.1, and 17.3 in J, H, and Ks-band, respectively. We construct JHK color-color and J/J-H and K/H-K color-magnitude diagrams to identify young stellar objects and estimate their masses. Based on these color-color and color-magnitude diagrams, a rich population of YSOs is identified which is associated with the W3 Main region. A large number of previously unreported red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main sequence stars with intrinsic color excesses. We find that the slope of the Ks-band luminosity function of W3 Main is lower than the typical values reported for the young embedded clusters. The derived slope of the KLF is the same as that found by Megeath et al. (1996), from which analysis by Megeath et al. indicates that the W3 Main region has an age in the range of 0.3--1 Myr. Based on the comparison between models of pre-main sequence stars with the observed color-magnitude diagram we find that the stellar population in W3 Main is primarily composed of low mass pre-main sequence stars. We also report the detection of isolated young stars with large infrared excesses which are most probably in their earliest evolutionary phases.

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arXiv2004

Detection of Knots and Jets in IRAS 06061+2151

We report detection of a Young Stellar Object with an evidence for an outflow in the form of knots in the molecular hydrogen emission line (2.121 micron) towards the massive star forming region IRAS 06061+2151. Near-infrared images reveal IRAS 06061+2151 to be a cluster of at least five sources, four of which seem to be early B type young stellar objects, in a region of 12 arcsec surrounded by a nebulosity. The presence of the knots that are probably similar to the HH objects in the optical wavelengths, suggests emerging jets from one of the cluster members. These jets appear to excite a pair of knot-like objects (Knot-NW and Knot-SE) and extend over a projected size of 0.5pc. The driving source for the jets is traced back to a member of the cluster whose position in the H-Ks/J-H color-color diagram indicates that it is a Class 1 type pre-mainsequence star. We also obtained K band spectra of the brightest source in the cluster and of the nearby nebular matter. The spectra show molecular hydrogen emission lines but do not show Brackett gamma line at 2.167 micron. These spectra suggest that the excitation of the molecular hydrogen lines is probably due to a mild shock.

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arXiv2003

A study of the Galactic star forming region IRAS 02593+6016 / S 201 in infrared and radio wavelengths

We present infrared and radio continuum observations of S 201 star forming region. A massive star cluster is observed in this region, which contains different classes of young stellar objects. The near-infrared colour-colour and colour-magnitude diagrams are studied to discuss the nature of these sources. We have discovered the knots of molecular hydrogen emission at 2.122 micron in the central region of S 201. These knots are clearly seen along the diffuse emission in north-west direction which are probably the obscured Herbig-Haro objects. High sensitivity and high resolution radio continuum images from GMRT observations at 610 and 1280 MHz show an interesting arc-shaped structure due to the interaction between the H II region and the adjacent molecular cloud. The ionization front at the interface between the H II region and the molecular cloud is clearly seen by comparing the radio, molecular hydrogen and Br Gamma images. The emission from the carriers of Unidentified Infrared Bands in the mid-infrared 6-9 micron (possibly due to PAHs) as extracted from the Midcourse Space Experiment survey (at 8, 12, 14 and 21 micron) is compared with the radio emission. The HIRES processed IRAS maps at 12, 25, 60, and 100 micron, have also been used for comparison. The spatial distribution of the temperature and the optical depth of the warm dust component around S 201 region, has been generated from the mid-infrared images.

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arXiv2003

A Ring Shaped Embedded Young Stellar (Proto)Cluster

We present sub-arcsec (FWHM ~ 0.5") J, H, K and L' images of a young stellar cluster associated with a candidate massive protostar IRAS22134+5834. The observations reveal a centrally symmetric, flattened cluster enclosing a central dark region. The central dark region is possibly a cavity within the flattened cluster. It is surrounded by a ring composed of 5 bright stars and the candidate massive protostar IRAS22134+5834. We construct JHKL' color-color and HK color-magnitude diagrams to identify the young stellar objects and estimate their spectral types. All the bright stars in the ring are found to have intrinsic infrared excess emission and are likely to be early to late B type stars. We estimate an average foreground extinction to the cluster of A_v \~ 5mag and individual extinctions to the bright stars in the range A_v ~ 20-40mag indicating possible cocoons surrounding each massive star. This ring of bright stars is devoid of any HII region. It is surrounded by an embedded cluster making this an example of a (proto)cluster that is in one of the dynamically least relaxed states. These observations are consistent with the recent non-axisymmetric calculations of Li & Nakamura, who present a star formation scenario in which a magnetically subcritical cloud fragments into multiple magnetically supercritical cores, leading to the formation of small stellar groups.

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arXiv2003

Mapping of Large Scale 158 micron [CII] Line Emission: Orion A

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 micron) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ~200 km/s and an angular resolution of 1.5'. During the first flight, an area of 30'x15' in Orion A was mapped. The observed [CII] intensity distribution has been compared with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and CO(3-2) from the literature. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV flux and volume density at a few selected positions.

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arXiv2003

Near-IR spectra of ISOGAL sources in the Inner Galactic Bulge

In this work we present near-IR spectra (HK-band) of a sample of 107 sources with mid-IR excesses at 7 and 15 $\rm μ$m detected during the ISOGAL survey. Making use of the DENIS interstellar extinction map from Schultheis et al. (1999) we derive luminosities and find that the $\rm M_{bol}$ vs.~$\rm ^{12}CO$ and $\rm M_{bol} vs. H_{2}O$ diagrams are powerful tools for identifying supergiants, AGB stars, giants and young stellar objects. The majority of our sample are AGB stars (~ 80%) while we find four good supergiant candidates, nine young stellar objects and 12 RGB candidates. We have used the most recent $\rm K_{0}-[15]$ relation by Jeong et al. (2002) based on recent theoretical modeling of dust formation of AGB stars to determine mass-loss rates. However, the uncertainties in the mass-loss rates are rather large. The mass-loss rates of the supergiants are comparable with those in the solar neighbourhood while the long-period Variables cover a mass-loss range from $\rm -5 < log \dot{\it{M}} < -7$. The red giant candidateslie at the lower end of the mass-loss rate range between $\rm -6.5 < log \dot{\it{M}} < -9$. We used the equivalent width of the CO bandhead at 2.3 $\rm μm$, the NaI doublet and the CaI triplet to estimate metallicities using the relation by Ram\'ırez et al. (\cite{Ramirez2000}). The metallicity distribution of the ISOGAL objects shows a mean [Fe/H] $\sim$ -0.25 dex with a dispersion of $\rm \pm 0.40 dex$ which is in agreement with the values of Ramírez et al. (\cite{Ramirez2000}) for Galactic Bulge fields between $\rm b = -4^{o}$ and $\rm b = -1.3^{o}$. A comparison with the solar neighbourhood sample of Lançon & Wood (LW) shows that our sample is ~ 0.5 dex more metal-rich on average.

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arXiv2003

Stellar sources in the ISOGAL intermediate bulge fields

We present a study of ISOGAL sources in the "intermediate" galactic bulge ($|$$l$$|$ $<$ 2$^\circ$, $|$$b$$|$ $\sim$ 1$^\circ$--4$^\circ$), observed by ISOCAM at 7 and 15 $μm$. In combination with near-infrared (I, J, K$_{\rm s}$) data of DENIS survey, complemented by 2MASS data, we discuss the nature of the ISOGAL sources, their luminosities, the interstellar extinction and the mass-loss rates. A large fraction of the 1464 detected sources at 15 $μm$ are AGB stars above the RGB tip, a number of them show an excess in ([7]-[15])$_{\rm 0}$ and (K$_{\rm s}$-[15])$_{\rm 0}$ colours, characteristic of mass-loss. The latter, especially (K$_{\rm s}$-[15])$_{\rm 0}$, provide estimates of the mass-loss rates and show their distribution in the range 10$^{-8}$ to 10$^{-5}$ M$_{\rm \odot}$/yr.

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arXiv2002

Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey

Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane in mainly four infrared bands between 6 and 25 micron. Two of these bands cover several Unidentified Infrared emission Bands (UIBs). With the aim of extracting the spatial distribution of the UIB emission on a large scale, a scheme has been developed to model the MSX data with emission in the UIBs alongwith the underlying thermal continuum from the interstellar dust. In order to test this scheme, a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152, Sh-156, Sh-186; Zavagno & Ducci 2001) for which imaging study in some individual UIBs is available from ISOCAM measurements, has been studied. The results of this comparative study on small angular scale are as follows : (i) the morphological details extracted from our scheme agree very well with those from the superior ISOCAM measurements; (ii) the integrated strength of UIBs extracted from the MSX database correlates extremely well with the sum of the strengths of individual UIBs measured from ISOCAM. This tight correlation is very encouraging and promises the potential of MSX database for study of large scale spatial distribution of UIB emission (and the carriers of UIBs) in the entire Galactic plane.

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arXiv2000

Massive and luminous YSO IRAS 05361+3539 and its environment. A study of star formation in the parent cloud - I

Near-infrared photometry and narrow/broad-band imaging of the massive and luminous young stellar object IRAS 05361+3539 are presented. Imaging observations were made at Mt. Abu while the photometric data were taken from the 2MASS. From the color-color and color-magnitude diagrams, we identified several sources of faint Class II type and about six Class I type in the parent molecular cloud complex. The IRAS 05361+3539 itself was seen to be a Class I object and our images in Br$γ$ and H$_{2}$ lines show jets/outflows from this object. The jet/outflow matches with the axis of CO outflow detected earlier. The near-infrared and the IRAS far-infrared flux distribution suggests a possible accretion disk with dust temperatures between 80 to 800K and extent of several tens to hundreds of AU. A possible FU Orionis type of source was detected in the cluster.

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arXiv1999

Efficient absolute aspect determination of a balloon borne far infrared telescope using a solid state optical photometer

The observational and operational efficiency of the TIFR 1 meter balloon borne far infrared telescope has been improved by incorporating a multielement solid state optical photometer (SSOP) at the Cassegrain focus of the telescope. The SSOP is based on a 1-D linear photo diode array (PDA). The online and offline processing schemes of the PDA signals which have been developed, lead to improvement in the determination of absolute telescope aspect ($\sim$ 0\farcm8), which is very crucial for carrying out the observations as well as offline analysis. The SSOP and its performance during a recent balloon flight are presented here.

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arXiv1999

New surveys of UBV photometry and absolute proper motions at intermediate latitude

A photometric and proper motion survey has been obtained in 2 directions at intermediate latitude: ($l=167.5^\circ$, $b=47.4^\circ$; $α_{2000}=9^h41^m26^s$,$δ_{2000}=+49^\circ53'27''$) and ($l=278^\circ$, $b=47^\circ$; $α_{2000}=11^h42^m56^s$, $δ_{2000}=-12^\circ31'42''$). The survey covers 7.13 and 20.84 square degrees, respectively. The limiting magnitude is about 18.5 in V for both directions. We have derived the density laws for stars (M$_{V}$ $\ge$ 3.5) as a function of distance from the galactic plane. The density laws for stars follow a sum of two exponentials with scale heights of 240 pc (thin disk) and 790 pc (thick disk), respectively. The local density of thick disk is found to be 6.1$\pm$3 % relative to the thin disk. The kinematical distribution of stars has been probed to distances up to 3.5 kpc above the galactic plane. New estimates of the parameters of velocity ellipsoid have been derived for the thick disk of the Galaxy. A comparison of our data sets with the Besan\c con model star count predictions has been performed, giving a good agreement in the magnitude range V = 13 to 18.

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arXiv1994

A Multicolor Survey of Absolute Proper Motions : Galactic Structure and Kinematics in the Direction of Galactic Center at Intermediate Latitude

We have derived a new photographic photometry and proper motions for 20000 stars with completeness to V = 18 in the direction of galactic center at the intermediate latitude (l = 3 deg,b = 47 deg; alpha(1950)=15h 18m, delta(1950) = +02deg 16') for a 15.5 sq deg field. The combination of four glass copies of the Palomar Observatory Sky Survey (i.e. POSS 1402 E&O and POSS 1429 E&O) has been used as a first epoch for proper motion determination. The random error of the proper motions is approximately 0.''3/cen to V=17. The photometric accuracy ranges between 0.07 to 0.10 in the V, B and U bands. We stress the importance of the magnitude and color effects in astrometric surveys of field stars. Using color-magnitude diagrams of a few cluster member stars, a new distance of 6.9+-0.5 kpc is derived for M5 and 20.3+-0.8 kpc for Pal 5 globular clusters. This is in good agreement with other determinations. We have analyzed the components of U+W and V galactic space motions resulting from the accurate proper motions survey. No dependence with z distance is found in the asymmetric drift of the thick disk population. New estimates of the parameters of the velocity ellipsoid have been derived for the thin disk, thick disk and halo populations of the Galaxy.

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