Engineering topics

Lada, Charles J.

Publications and source records attributed to Lada, Charles J..

At least 19 records

NASA NTRS2005

Infrared Extinction and the Initial Conditions for Star and Planet Formation

This grant funded a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program were to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) use the results to measure and quantitatively describe the physical conditions of the dense gas and dust that produce stars and their accompanying planetary systems in molecular clouds. The goals of this project were met and exceeded as described below. 1) The infrared data for the project were obtained in a number of observing runs using the 3.5-meter NTT and 8-meter VLT telescopes of the European Southern Observatory in Chile and the 1.2-meter telescope of the Smithsonian Astrophysical Observatory in Arizona, the 1 0-meter Keck telescope in Hawaii, the 6.5-meter MMT of the Smithsonian Astrophysical Observatory in Arizona, and the NASA Hubble Space Telescope. The molecular-line data was obtained in three runs using the IRAM 30-meter telescope in Spain and one run with the ESO-15 meter millimeter-wave telescope in Chile. Millimeter-wave continuum measurements were obtained with the 15-meter JCMT in Hawaii. 2) Considerable effort was expended to reduce the infrared imaging observations including the development of custom software to produce high quality photometry and source astrometry. All the millimeter-line data was reduced using standard reduction routines. The highlights of the infrared analysis were the production of detailed extinction maps and the construction of profiles of the density structure of the B68, Coalsack, B335 and Lupus clouds. 3) The principal scientific accomplishments of this research program include the following: We were able to use our infrared observations to determine the density structure of the B68 cloud to an unprecedented level of precision. This lead to a major breakthrough in the study of molecular cloud structure. For the first time we have been able to characterize the structure of a dark cloud in a detail only exceeded by that known for a star. We determined that the cloud's structure is exquisitely well described by the equations of a Bonner-Ebert sphere (a pressure confined isothermal sphere). We were able to show that the cloud is very nearly in equilibrium with the internal thermal pressure of the cloud balancing gravity and the external pressure of the surrounding interstellar medium. We were able to determine for the first time the gas-to-dust ratio in a dense cloud core. We also demonstrated a new method to determine extremely precise distances to such clouds by combining knowledge of the properties of Bonner-Ebert Spheres with our infrared and millimeter-wave observations.

Lada, Charles J.↗

NASA NTRS2005

Measuring the Internal Structure and Physical Conditions in Star and Planet Forming Clouds Core: Toward a Quantitative Description of Cloud Evolution

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular cloud cores and investigate the physical conditions which give rise to star and planet formation. The goals of this program are to acquire, reduce and analyze deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds in order to internal structure of starless cloud cores and to quantitatively investigate the evolution of such structure through the star and planet formation process. During the second year of this grant, progress toward these goals is discussed.

Lada, Charles J.↗

NASA NTRS2004

Infrared Extinction and the Initial Conditions for Star and Planet Formation

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program are to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) prepare results, where appropriate, for publication. A description of how these goals were met are included.

Lada, Charles J.↗

NASA NTRS2004

Measuring the Internal Structure and Physical Conditions in Star and Planet Forming Clouds Cores: Towards a Quantitative Description of Cloud Evolution

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular cloud cores and investigate the physical conditions which give rise to star and planet formation. The goals of this program are to acquire, reduce and analyze deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds in order to determine the detailed initial conditions for star formation from quantitative measurements of the internal structure of starless cloud cores and to quantitatively investigate the evolution of such structure through the star and planet formation process.

Lada, Charles J.↗

NASA NTRS2003

Infrared Extinction and the Initial Conditions For Star and Planet Formation

Lada, Charles J.↗

NASA NTRS2002

Infrared Extinction and the Initial Conditions for Star and Planet Formation

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program are to: (1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds; (2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds; and (3) prepare results, where appropriate, for publication.

Lada, Charles J.↗

NASA NTRS2002

Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

Greene, Thomas P.↗

NASA NTRS1997

Summer Workshop on the Origins of Stars and Planets

The meeting had broad representation from both the national and international scientific communities. There were 38 oral lectures describing the latest research results pertaining to star and planet formation in young clusters presented at the workshop. In addition there were 65 poster papers describing research in this area also presented at the workshop. Because there was ample space made available by Wellesley College, all posters were up and available throughout the entire duration of the meeting. This insured more than adequate time for all participants to view the posters and interact with their authors. The oral talks were 15 minutes in duration with an additional 15 minutes reserved for questions and discussion. As a result there was considerable discussion and exchange of ideas which insured that the workshop nature of the conference was maintained despite the large attendance. In summary, the workshop was a great success scientifically while at the same time being extremely cost effective. The 1996 workshop exceeded the overall objectives originally set for it.

Lada, Charles J.↗

NASA NTRS1994

Dust extinction and molecular gas in the dark cloud IC 5146

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

Lada, Charles J.↗

NASA NTRS1993

Infrared images of the young cluster NGC 2264

Initial results of an extensive IR imaging survey of the young cluster NGC 2264 and a nearby galactic control field are presented. A large portion of the cluster was imaged in each of the three standard near-IR colors (J, H, and K) with an IR array camera. On the basis of a comparison of these observations, the size of the cluster population is estimated, and the nature of its members is investigated. The cluster is found to contain 360 +/- 130 members. The slope of the K luminosity function of the cluster is significantly steeper than that expected for a cluster of ZAMS stars, and appears to flatten out or turn over at an apparent K magnitude of roughly 13.0-14.0. An analysis of the JHK color-color diagrams of the cluster and control fields shows that approximately 170 sources observed toward the cluster have colors indicative of intrinsic excess IR emission.

Lada, Charles J.↗

NASA NTRS1992

IRAS observations of young stellar objects in the Corona Australis dark cloud

The young stellar object (YSO) population associated with the dark cloud complex in Corona Australis is studied by synthesizing IRAS data with newly obtained near-IR and mid-IR photometry and previously published optical/IR data. Twenty-four YSOs in the Cr A complex are identified. The observed range of spectral energy distribution shapes and bolometric luminosities are consistent with those observed in other dark clouds. The duration and efficiency of star formation are found to be similar to the Rho Ophiuchi IR cluster. The low number of YSOs compared to other dark clouds is understood by a reevaluation of the molecular mass of the R Cr A cloud which shows it to be much less massive than previously assumed.

Wilking, Bruce A.↗

NASA NTRS1991

Star formation and the nature of bipolar outflows

This paper presents a simple physical model for the bipolar molecular outflows that frequently accompany star formation. The model forges an intrinsic link between the bipolar flow phenomenon and the process of star formation, and it helps to explain many of the systematics known for existing sources.

Shu, Frank H.↗

NASA NTRS1991

The nature, origin and evolution of embedded star clusters

The recent development of imaging infrared array cameras has enabled the first systematic studies of embedded protoclusters in the galaxy. Initial investigations suggest that rich embedded clusters are quite numerous and that a significant fraction of all stars formed in the galaxy may begin their lives in such stellar systems. These clusters contain extremely young stellar objects and are important laboratories for star formation research. However, observational and theoretical considerations suggest that most embedded clusters do not survive emergence from molecular clouds as bound clusters. Understanding the origin, nature, and evolution of embedded clusters requires understanding the intimate physical relation between embedded clusters and the dense molecular cloud cores from which they form.

Lada, Charles J.↗

NASA NTRS1990

A spectacular molecular outflow in the Monoceros OB1 molecular cloud

Detailed observations of CO, CS, IR continuum, and H2 emission from a large, highly collimated, bipolar outflow in the Monoceros OB1 molecular cloud are presented. The CO observations suggest that molecular gas in the outflow is contained in a shell with higher velocity material situated interior to lower velocity material. The velocities of outflow emission are found to increase with increasing distance from the center of the outflow. Additional detections include shock-excited molecular hydrogen emission from the blueshifted lobe of the outflow and six 2-micron sources in the direction of the outflow. Near-IR and IRAS observations suggest that the driving source for the outflow must have a bolometric luminosity below about 4.5 solar luminosities. It is concluded that the flow is probably not driven by stellar radiation from a central source.

Margulis, Michael↗

NASA NTRS1989

Young stellar objects in the Monoceros OB1 molecular cloud

Detailed results of an IRAS survey of a large portion of the Monoceros OB1 molecular cloud for discrete far-IR sources are presented. IRAS spectral energy distributions are constructed for 27 of the 30 sources identified in the region. Many are bright class I energy distributions, indicating that star formation is still occurring in the complex which produced the visible cluster, NGC 2264. Far-IR luminosities are calculated for each source, and the bolometric luminosity functions for class I and class II sources in the Mon OB1 cloud are found to be significantly different. Of all class I and II sources more luminous than 5 solar, 50 percent of class I sources are more luminous than 60 solar while only 4 percent of class II sources are. An attempt is made to determine the type of young stellar object in the cloud with which molecular outflows are associated.

Margulis, Michael↗

NASA NTRS1989

IRAS observations of the Rho Ophiuchi infrared cluster - Spectral energy distributions and luminosity function

High-sensitivity IRAS coadded survey data, coupled with new high-sensitivity near-IR observations, are used to investigate the nature of embedded objects over an 4.3-sq-pc area comprising the central star-forming cloud of the Ophiuchi molecular complex; the area encompasses the central cloud of the Rho Ophiuchi complex and includes the core region. Seventy-eight members of the embedded cluster were identified; spectral energy distributions were constructed for 53 objects and were compared with theoretical models to gain insight into their evolutionary status. Bolometric luminosities could be estimated for nearly all of the association members, leading to a revised luminosity function for this dust-embedded cluster.

Wilking, Bruce A.↗

NASA NTRS1988

Molecular outflows in the Monoceros OB1 molecular cloud

Observations of J = 1-0 emission from CO in nine suspected molecular outflows in the Monoceros OB1 molecular cloud are presented. It is found that, if the five sources which are confirmed to be outflows conserve momentum as they evolve, they will sweep up at least 0.6 percent of the mass of the entire cloud before coming into pressure equilibrium with the ambient gas. This number indicates that it should take at most 160 episodes of similar outflow activity in order to sweep up the bulk of the Mon OB1 cloud to highly supersonic speeds.

Margulis, Michael↗

NASA NTRS1988

The small molecular cloud toward HD 169454

Optical absorption line observations of the B1 supergiant HD 169454 reveal the presence of an intervening translucent interstellar cloud. Millimeter wavelength observations of CO emission show that the absorption lines can be attributed to a well-defined cloud approximately 18 by 22 min in extent at the same radial velocity as the C2 and CN absorption lines. The map of the CO emission shows three large condensations and evidence of unresolved structure on smaller scales. Various procedures for determining the cloud mass are compared. The estimated mass is 7-14 M solar masses if the cloud lies at the distance (D about 125 pc) of an extended atomic cloud at the same radial velocity, and is 250-500 M solar masses if the kinematic distance (D about 750 pc) is adopted. The dynamical state of the cloud is examined. The composition and structure of the cloud are discussed with reference to detailed theoretical models and the properties of other interstellar clouds.

Jannuzi, Buell T.↗