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A Spectroscopic and Photometric Survey of Stars in the Field of L1457: A New Distance Determination
We present a spectroscopic and photometric survey of a sample of fieldstars in the region of the molecular cloud L1457. High-qualitycoudé feed spectra, together with five-band photometry in theSloan Digital Sky Survey system and near-infrared archival data from theTwo Micron All Sky Survey, are used to derive color excesses anddistances for the stars. Based on these data, a new distance estimate of360+/-30 pc is derived for the cloud, supporting recent results by K. L.Luhman. The data further indicate that the north-south velocity gradientseen in the millimeter-wave CO data is mirrored in a distance gradient,with the northern part of the cloud being closer to us. A second, lessopaque, layer of extinction is detected at ~80 pc. This distance isconsistent with the earlier distance estimates to the cloud, based on NaI absorption. We identify this layer with the wall of the hot LocalBubble. Hence, the dense cloud is not, as previously thought, associatedwith the Local Bubble.
| Photometric Investigation of the MBM 12 Molecular Cloud Area in Aries. II. Cloud Distance
Photoelectric magnitudes and color indices in the Vilnius seven-colorsystem for 152 stars are used to investigate the interstellar extinctionin the area of the Aries molecular cloud MBM 12, coinciding with theL1454 and L1457 dust clouds. Spectral types, absolute magnitudes, colorexcesses, interstellar extinctions and distances of the stars aredetermined. The plot of interstellar extinction A_V versus distanceshows that the dust cloud is situated at a distance of 325 pc, at 180 pcfrom the Galactic plane, and its true diameter is about 11 pc. Theinterstellar extinction law in the area is found to be normal, typicalfor the diffuse dust. Ten peculiar or unresolved binary stars and someheavily reddened stars are detected.
| Photometric Investigation of the MBM 12 Molecular Cloud Area in Aries. I. Photoelectric Photometry
The results of photoelectric photometry in the Vilnius seven-colorsystem are given for 152 stars down to 12.2 mag in the area of themolecular cloud MBM 12 and the dust clouds L1454 and L1457 in Aries. Theresults of photometric classification of stars are also given. Theinvestigation of interstellar extinction in the area is described in thenext paper.
| The distance to the nearest star-forming clouds: MBM12 and MBM20
We present high-resolution spectra (R ~ 49,000) of stars that haveparallax measurements from the Hipparcos satellite and are projectedalong the line of sight to the two nearest known star forming clouds tothe Sun: MBM12 and MBM20. The spectra were obtained with the FOCESEchelle Spectrograph at the 2.2 meter telescope in Calar Alto, Spain andthe wavelength range was chosen to include the interstellar Na I D linesat lambda 5889.950 Ä and lambda 5895.924 Ä. Since the starsare at a range of distances, we use their spectra along with theirparallaxes from Hipparcos to determine the distance to the moleculargas. The stars in front of the cloud do not show interstellar Na I Dabsorption features while the stars behind the cloud do showinterstellar absorption features. We find that both clouds are somewhatmore distant than previously estimated. The revised distance to MBM12 is58+/-5 pc < d < 90+/-12 pc and the distance to MBM20 is 112+/-15pc < d < 161+/-21 pc.
| ROSAT PSPC observations of T Tauri stars in MBM12 PSPC observations of T Tauri stars in MBM12
We present the ROSAT PSPC pointed and ROSAT All-Sky Survey (RASS)observations and the results of our low and high spectral resolutionoptical follow-up observations of the T Tauri stars (TTS) and X-rayselected T Tauri star candidates in the region of the high galacticlatitude dark cloud MBM12 (L1453-L1454, L1457, L1458). Previousobservations have revealed 3 ``classical'' T Tauri stars and 1``weak-line'' T Tauri star along the line of sight to the cloud. Becauseof the proximity of the cloud to the sun, all of the previously knownTTS along this line of sight were detected in the 25 ks ROSAT PSPCpointed observation of the cloud. We conducted follow-up opticalspectroscopy at the 2.2-meter telescope at Calar Alto to look forsignatures of youth in additional X-ray selected T Tauri starcandidates. These observations allowed us to confirm the existence of 4additional TTS associated with the cloud and at least 2 young mainsequence stars that are not associated with the cloud and place an upperlimit on the age of the TTS in MBM12 ~ 10 Myr. The distance to MBM12 hasbeen revised from the previous estimate of 65+/-5 pc to 65+/-35 pc basedon results of the Hipparcos satellite. At this distance MBM12 is thenearest known molecular cloud to the sun with recent star formation. Weestimate a star-formation efficiency for the cloud of 2-24%. We havealso identified a reddened G9 star behind the cloud with A_v ~ 8.4-8.9mag. Therefore, there are at least two lines of sight through the cloudthat show larger extinctions (A_v > 5 mag) than previously thoughtfor this cloud. This higher extinction explains why MBM12 is capable ofstar-formation while most other high-latitude clouds are not. Table~4 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.}
| The magnetic field in LYNDS 1457: Multiband photopolarimetry
We have performed multiband photopolarimetry toward stars behind themolecular cloud L1457 (MBM 12). This cloud is the nearest knownmolecular cloud (65 pc) and thought to be contained within the local'hot bubble.' The polarization shows a regular structure, indicatingthat the cloud is threaded by an ordered magnetic field. The wavelengthdependence of the polarization seems to indicate that the grains inL1457 have higher indices of refraction than normal for interstellarclouds. However, the wavelength of maximum polarization indicates thattheir size distribution is close to normal.
| Polarization measurements of stars in the region of the nearby molecular cloud MBM 12
Linear polarization measurements of stars in the region of the nearbyhigh-latitude molecular cloud MBM 12 are presented. Stars behind thecloud show a polarization of about 2-3 percent, while stars that are infront of the cloud or are projected outside the cloud boundary show verylow values (less than 0.5 percent) of polarization. If the polarizationis caused by dust grains aligned by a magnetic field, the observedpolarization position angles suggest that the field in the cloud is moreor less unidirectional and is roughly parallel to the long axis of thecloud. The cloud magnetic field has a direction that is significantlydifferent from that of the local interstellar field, and its strengthmay be as large as about 60 microG.
| On the nearest molecular clouds. II - MBM 12 and 16
The paper presents echelle spectra recorded at the D lines of Na I forthree stars projected on the high-latitude molecular cloud MBM 16 at l =172 deg, b = -38 deg. The A stars HD 21142 at about 95 pc and HD 21134at about 240 pc show strong D-line absorption at the same velocities asthe CO emission observed at these positions. The distance to MBM 16therefore is in the range of 60 to 95 pc. MBM 16 is only 11 deg awayfrom MBM 12, previously placed by the same method at distance of about65 pc. Consideration is given to the relationship between clouds 12 and16 and the local hot low-density interstellar gas.
| A molecular cloud in the local, hot interstellar medium
Echelle spectra recorded at the D lines of Na I are reported for nine Aor F stars. Lying at approximate distances ranging from 25 to 230 pc,the stars are projected on or near the high-latitude molecular cloud MBM12 at l = 159 deg, b = -34 deg. Among a subgroup of five of these starsseparated by no more than 1.2 deg on the sky, four which are located atdistances d more than 70 pc show strong interstellar D line absorptionnear the radial velocity of the CO emission observed in this generaldirection. The fifth star, at roughly 60 pc, shows no detectableabsorption. MBM 12 therefore probably lies at roughly 65 pc, within thelocal region filled primarily by very hot, low-density gas, a conclusionsupported by the large internal velocity dispersion of the molecularcloud complex.
| Derivation of angular diameters of stars from lunar occultations
A description is presented of the results obtained in the photoelectricobservations of occultations involving four stars. The considered starsinclude Eta Gem (ZC 946), Mu Gem (ZC 976), 187 B. Gem (ZC 1161), and 31Leo (ZC 1486). The theoretical principles of the studies are considered,taking into account point source occultations, the stellar diameter andthe influence of telescope aperture, and spectral effects. Observationaldata concerning the considered stars are presented in a table and anumber of graphs. It is pointed out that Mu Gem is a triple system.However, on account of their distances and their weakness the companionscannot affect the observed intensity curve. A combination of the deriveddiameter with the trigonometric parallax reported by Jenkins (1963)provides for the linear diameter of Mu Gem the result of 91 plus orminus 28 solar diameters.
| Observations of occultations of stars by the moon
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...13..395H&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Овен |
| Прямое восхождение: | 02h55m05.10s |
| Склонение: | +20°48'00.8" |
| Видимая звёздная величина: | 8.833 |
| Собственное движение RA: | 20.3 |
| Собственное движение Dec: | -5.8 |
| B-T magnitude: | 9.347 |
| V-T magnitude: | 8.876 |
Каталоги и обозначения:
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