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J/ApJ/438/813      Stellar population in ρ Oph cloud core     (Strom+, 1995)

The evolutionary status of the stellar population in the ρ Ophiuchi cloud core STROM K.M., KEPNER J., STROM S.E. <Astrophys. J. 438, 813 (1995)> =1995ApJ...438..813S (SIMBAD/NED BibCode)
ADC_Keywords: Regional catalog; Positional data; Photometry, infrared; Cross identifications Keywords: circumstellar matter - infrared: stars - ISM: individual (ρ Ophiuchi) - stars: luminosity function, mass function - stars: pre-main-sequence - surveys Abstract: This contribution reports the results of an infrared imaging survey aimed at characterizing the stellar populations associated with the three densest star-forming cores in the Ophiuchus molecular cloud complex. The survey has sufficient sensitivity at J, H, and K (at 5σ limits of 16.5, 15.4 and 14.2) to provide a complete census of embedded young stellar objects (YSOs) with masses greater than the hydrogen-burning limit, provided that their ages are less than 3 Myr and that they are obscured by no more than ∼18 mag of visual extinction. Our data suggest (1) a large fraction (>70%) of the sources located within the cores are still surrounded by circumstellar disks and/or envelopes; and (2) the shape of the initial mass function for masses, M<1Msun, appears to be consistent with that derived from the solar neighborhood. We also report the results of a deeper imaging survey of centimeter continuum sources (14 sources) in these star-forming cores and in the larger Ophiuchus complex (eight sources). A large fraction 11/14) of the radio sources associated with the cores appear to have infrared excesses diagnostic of circumstellar accretion disks and/or infalling circumstellar envelopes. In these cases, the centimeter continuum radiation most likely diagnoses the ionized component of energetic winds or jets which characterize YSOs during the disk accretion phase. By contrast, of the eight radio sources located outside dense cores, only two show infrared excesses. For the sources which lack infrared excesses, the centimeter continuum emission is probably produced by gyrosynchrotron radiation arising in the stellar magnetospheres of weak emission T Tauri stars. There is some evidence that the frequency of binary companions among the sample of centimeter continuum sources in the molecular cores may be higher (by as much as a factor of 3-4) than that among the older, distributed population of young stars in the larger Ophiuchus cloud complex. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1 81 52 Photometry data from the SQIID Mosaic table2 69 52 Derived values from the SQIID data table3 81 67 Data for stars with photometry of lower accuracy table4 87 93 Infrared data for the ρ Ophiuchi cloud VLA sources table6 72 5 Multiplicity measures of VLA sources
Table 5: Identified pairs in the VLA sample (LFAM: Leous et al. 1991) ------------------------------------------------------------------- Primary Secondary Sep. AK Core ------------------------------------------------------------------- LFAM 2 LFAM 1 9"7 3.8 A S 2 LFAM 3 10"6 3.1 A LFAM 5 LFAM 4 9"7 A LFAM 9SW LFAM 9NE 1"2 0.5 A LFAM 15N LFAM 15S 6"3 0.05 A LFAM 33 LFAM 33N 7"3 2.75 E/F LFAM 30E LFAM 30W 3"3 0.3 E/F LFAM 30S 3"9 2.5 E/F ------------------------------------------------------------------- Multiple VLA Sources in Cores Outside the LFAM Survey ------------------------------------------------------------------- WL 5 YLW 12A 6"5 1.1 B ------------------------------------------------------------------- Multiple VLA Sources in All Cores with Separation Below 1" ------------------------------------------------------------------- S1 A S1 B 0"02 1.8 A SR 12A SR 12B 0"30 0.1 E/F VSSG 14A VSSG 14B 0"10 0.8 B ------------------------------------------------------------------- Byte-by-byte Description of file: table1 table3
Bytes Format Units Label Explanations
1- 2 I2 h RAh Right ascension (1950) 4- 5 I2 min RAm Right ascension (1950) 7- 10 F4.1 s RAs Right ascension (1950) 14 A1 --- DE- Declination sign 15- 16 I2 deg DEd Declination (1950) 18- 19 I2 arcmin DEm Declination (1950) 21- 22 I2 arcsec DEs Declination (1950) 25- 29 F5.2 mag Kmag K magnitude 32- 35 F4.2 mag e_Kmag ? Error on K magnitude 37 A1 --- l_J-H [><] Limit flag on J-H 38- 41 F4.2 mag J-H ? J-H colour index 42 A1 --- n_J-H [b] See Note (1) 44- 47 F4.2 mag e_J-H ? Error on J-H 51 A1 --- l_H-K [><] Limit flag on H-K 52- 55 F4.2 mag H-K ? H-K colour index 56 A1 --- n_H-K [b] See Note (1) 58- 61 F4.2 mag e_H-K ? Error on H-K 64- 66 A3 --- Core Dense molecular core association (2) 69- 71 A3 --- Type Type of stars (3) 73 A1 --- n_Id [a] See Note (4) 74- 81 A8 --- Id Identification
Note (1): When 'b': This object falls on a small gap in the H mosaic. J=16.15±0.20. Note (2): A = Oph A B = Oph B E/F= Oph E/F Note (3): P= Photospheric; Stars which fall within the domain of the normal, reddened main-sequence dwarfs D= Disk; Stars which fall redward of the reddening vector extending from the latest main-sequence dwarfs but blueward of the reddening vector extending upward from the reddest colors predicted for an optically thick, physically thin accretion disk E= Envelope; Stars which lie rightward of reddened accretion disk colors Stars which lie within 1σ of a domain boundary are denoted P/D or D/E. Note (4): When 'a': These objects are nebulous, and the photometric center shifts with wavelengths
Byte-by-byte Description of file: table2
Bytes Format Units Label Explanations
1- 2 I2 h RAh Right ascension (1950) 4- 5 I2 min RAm Right ascension (1950) 7- 10 F4.1 s RAs Right ascension (1950) 14 A1 --- DE- Declination sign 15- 16 I2 deg DEd Declination (1950) 18- 19 I2 arcmin DEm Declination (1950) 21- 22 I2 arcsec DEs Declination (1950) 25- 28 F4.2 mag J10 ? Derived reddening-corrected absolute J magnitude 31- 34 F4.2 mag A1J ? Extinction A1J (1) 37- 40 F4.2 mag J20 ? Reddening-corrected absolute J magnitude (2) 43- 46 F4.2 mag A2J ? Extinction A2J (2) 49 A1 --- l_Mass0.3 Limit flag on mass 50- 53 F4.2 solMass Mass0.3 ? Mass derived from D'Antona and Mazzitelli (1994) tracks assuming a cluster age of 0.3Myr 54 A1 --- n_Mass0.3 [f] foreground 55 A1 --- l_Mass1 Limit flag on mass 56- 59 F4.2 solMass Mass1 ? Mass derived from D'Antona and Mazzitelli (1994) tracks assuming a cluster age of 1Myr 60 A1 --- n_Mass1 [f] foreground 62- 69 A8 --- Id Identification
Note (1): Derived from the (J-H), (H-K) diagram for stars whose reddened colours place them within the domain occupied by stars surrounded by accretion disk Note (2): Derived from the J, (J-H) color-magnitude diagram for objects which lie within the domain occupied by normal reddening stars; an isochrone corresponding to an age of 0.3Myr is assumed in estimating A2J
Byte-by-byte Description of file: table4
Bytes Format Units Label Explanations
1- 8 A8 --- Object Object 11 A1 --- l_Jmag [>] Limit flag on J magnitude 12- 16 F5.2 mag Jmag ? J magnitude 17 A1 --- q_Jmag [ABCD] Error on J magnitude (1) 19 A1 --- l_Hmag [>] Limit flag on H magnitude 20- 24 F5.2 mag Hmag ? H magnitude 25 A1 --- q_Hmag [ABCD] Error on H magnitude (1) 28 A1 --- l_Kmag [>] Limit flag on Kmag 29- 33 F5.2 mag Kmag ? K magnitude 34 A1 --- q_Kmag [ABCD] Error on K magnitude (1) 36 A1 --- l_L'mag Limit flag on L' magnitude 37- 41 F5.2 mag L'mag ? L' magnitude 42 A1 --- q_L'mag [ABCD] Error on L' magnitude (1) 43 A1 --- l_Mmag [>] Limit flag on Mmag 44- 48 F5.2 mag Mmag ? M magnitude 49 A1 --- q_Mmag [ABCD] Error on M magnitude (1) 51 A1 --- l_J-H [>] Limit flag on J-H 52- 56 F5.2 mag J-H ? J-H colour index 57 A1 --- u_J-H Uncertainty flag on J-H 58 A1 --- l_H-K [>] Limit flag on H-K 59- 62 F4.2 mag H-K ? H-K colour index 63 A1 --- u_H-K Uncertainty flag on H-K 64 A1 --- l_K-L' [><] Limit flag on K-L' 65- 68 F4.2 mag K-L' ? K-L' colour index 69 A1 --- u_K-L' Uncertainty flag on K-L' 71- 74 F4.2 mag K-M ? K-M colour index 75 A1 --- u_K-M Uncertainty flag on K-M 77- 87 A11 --- Notes Notes (2)
Note (1): The quality index is defined as: A, uncertainty <10%; B, uncertainty between 10 and 20%; C, uncertainty between 20 and 30%; D, the uncertainty is probably larger than 30%, not due to photon statistics, but due to other problems such as close companions and problems dealing with a very nonflat background. Note (2): Keys to notes: (1): Objects 1 and 2 correspond to GSS 30 NIRS 3 and 2 of Tamura et al. 1991. They lie within the reflection nebulosity surrounding GSS 30 complicating measurement of the fluxes attributable to these objects. They are separated by 11"6. Object 2 is also IRS 2 of Castelaz et al.1985 (2): Reflection nebulosity is associated with this object. A bright star (K=7.3) lies 10"4 away at P.A. 145deg (3): This pair is separated by 1"15 at P.A. 67deg (4): This object illuminates a large reflection nebulosity in the near-infrared as well as on the POSS red plate (5): These objects are separated by 6"3 at P.A. 170deg. The northern object lies nearest to the VLA position (6): The L' and M magnitudes were measured on the night following the J, H, and K measurements (7): The lunar occultation observation of Simon et al. 1987 and the speckle observations of Zinnecker, Chelli & Perrier 1987 require two components. The best-fit model of Simon et al.1987 requires 85% of the light at K in an object of 7.1 mas diameter and 15% of the light in a halo of 415 mas diameter. A reflection nebula is associated with this object (8): This object resolves into a close triple. 30W is at 3.3" at P.A. 269deg from 30E. 30S is at 3.9" at P.A.232deg from 30E. Both Barsony et al 1989 and Rieke, Ashok, & Boyle 1989 had found this object to be double (9): This object also illuminates a reflection nebula. The secondary lies at 7.3" at P.A. 323deg (10): Owing to a slight telescope drift, this northern component only appeared in the L' and M frames of object 33. However, the J, H, and K magnitudes can be measured on our SQIID frames. Those values are given here for completeness (11): Lunar occultation studies (Simon et al.1987) have resolved this object. No Fresnel interference was seen; this object could be modeled with geometrical optics. A satisfactory fit to the observations could be made with a uniformly illuminated object of ∼0.5" extent. This object illuminates a reflection nebula; the nearest neighbors of this object lie at 26.2" at PA 48deg (K=10.6) and 23.3" at P.A. 297deg (K=10.5). This nebulosity and the companions have been discussed by Zinnecker 1989. The polarization of the nebulosity has been studied by Aspin, Casali & Walther 1989 (12): These objects have been detected in previous VLA surveys of the ρ Oph cloud and are also located in core regions. They are included here as we obtained new data over the full wavelength range (13): Also known as El 27 and is a 3 in the list of LFAM (Leous et al. 1991) (14): Denoted a6 in the list of LFAM (Leous et al. 1991)
Byte-by-byte Description of file: table6
Bytes Format Units Label Explanations
1- 47 A47 --- Sample Sample 50- 53 F4.2 --- mf Multiplicy frequency (1) 56- 59 F4.2 --- cp Companion probability (2) 62- 65 F4.2 --- pf Pairing factor (3) 67- 68 I2 --- N Number of sources 72 I1 --- Notes ? Notes (4)
Note (1): Defined as the ratio between the number of multiple systems detected and the number of all objects (single+multiple) observed. See Appendix in the paper Note (2): Defined as the ratio between the number of stellar components in multiple systems and the number of stellar components in all objects observed. See Appendix in the paper Note (3): Defined as the ratio between the number of pair and the number of multiple systems. See Appendix in the paper Note (4): Keys to notes: 1: N is the number of sources imaged at the Infrared Telescope Facility which were bright enough at K to allow a companion fainter by at least 3 mag to be detected 2: While there are 35 sources in the LFAM 5sigma sample, four of these can be found in two pairs using our definition Of pairs. Therefore the total sample must be reduced by two systems 3: Four of the LFAM sources fall along a line centered on a source which they feel is a background galaxy. These objects have been eliminated from this sample as they are probable background objects 4: This sample includes the eight 3σ near-infrared identified objects while eliminating the probable background objects
References: Aspin C., Casali M.M., Walther D.M. 1989, in Proc. ESO Workshop on Low-Mass Star Formation and Pre-Main-Sequence Objects, ed. B. Reipurth (Garching: European Southern Obs.), 349 Barsony M. et al. 1989, ApJ 346, L93 Castelaz M.W. et al. 1985, ApJ 290, 261 D'Antona F. and Mazzitelli I. 1994, ApJS 90, 467 Leous J.A. et al. 1991, ApJ 379, 683 (LFAM) Rieke G.H., Ashok N.M., Boyle R.P. 1989, ApJ 339, L71 Simon M. et al. 1987, ApJ 320, 344 Tamura M. et al. 1991, ApJ 378, 611 Zinnecker H. 1989, in Proc. ESO Workshop on Low-Mass Star Formation and Pre-Main-Sequence Objects, ed. B. Reipurth (Garching: European Southern Obs.), 447 Zinnecker H., Chelli A., Perrier C. 1987, in IAU Symp. 115, Star Forming Regions, ed. M. Peimbert and J. Jugako (Dordrecht: Reidel), 71 Historical Notes: Keypunched at CDS
(End) James Marcout, Simona Mei [CDS] 08-Aug-1995
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