Mag Star Research Articles

Calibration of HST wide field camera for quantitative analysis of faint galaxy images

We present the methods adopted to optimize the calibration of images obtained with the Hubble Space Telescope (HST) Wide Field Camera (WFC) (1991-1993). Our main goal is to improve quantitative measurement of faint images, with special emphasis on the faint (I approximately 20-24 mag) stars and galaxies observed as a part of the Medium-Deep Survey. Several modifications to the standard calibration procedures have been introduced, including improved bias and dark images, and a new supersky flatfield obtained by combining a large number of relatively object-free Medium-Deep Survey exposures of random fields. The supersky flat has a pixel-to-pixel rms error of about 2.0% in F555W and of 2.4% in F785LP; large-scale variations are smaller than 1% rms. Overall, our modifications improve the quality of faint images with respect to the standard calibration by about a factor of five in photometric accuracy and about 0.3 mag in sensitivity, corresponding to about a factor of two in observing time. The relevant calibration images have been made available to the scientific community.

WFPC2 observations of the globular cluster M30

We describe images of the center of the dense globular cluster M30 (NGC 7099) obtained with the Hubble Space Telescope Wide Field/Planetary Camera 2 (HST WFPC2). Data taken in the F336W, F439W, and F555W filters (approximately U, B, and V) yield a color-magnitude diagram with photometric errors of 1 sigma = 0.05 mag for stars with V less than 17.5, and 1 sigma approximately 0.1 mag at V = 20, which is 1.5 mag fainter than the main-sequence turnoff. Simulations show that the star identifications are essentially complete for stars with V less than 19.5, even in the densest regions of the cluster. The projected radial distribution of stars can be represented by a power law distribution: N(r) approximately r(exp alpha), with slope alpha = -0.4 +/- 0.15, into radii less than 0.4 sec (0.015 pc). The radial profile is also consistent with a flat core of any radius smaller than approximately 1.5 sec (0.05 pc), but inconsistent with any core radius larger than 2.5 sec (0.09 pc). A total of 30 blue straggler candidates within 20 sec of the cluster center have been identified from the three-color data. Their radial distribution is strongly centrally concentrated when compared to the horizontal branch, red giant branch, or main-sequence stars in the cluster. The abundance of blue stragglers (relative to red giants and subgiants) within r approximately less than 20 sec of the center of M30 is f(sub BS) = 0.19 =/- 0.04, about twice as high as in other dense clusters.

A catalog of blue and red supergiants in M33

We present a catalog of blue and red stars in M33 based on photographic photometry of over 65,000 objects extracted from plates taken with the 3.6 m Canada-France-Hawaii Telescope (CFHT) and the 2.0 m Rozhen (Bulgarian) Telescope. The completeness limit of the various surveys are estimated here to be V = 19.5 mag for those stars situated in crowded associations, and V = 20.0 mag for stars in the interarm fields. We list magnitudes and positions for 2112 blue stars, defined by (U - V) less than 0.0 mag, (U - B) less than 0.0 mag, and V less than 19.5 mag, and 389 red stars defined by (B - V) greater than 1.8 mag and V less than 19.5 mag. Of these, 1156 are candidate O stars on the basis of (U - V) less than -0.9 mag.

The Importance of Accurate Positions in the QSO Story

Who discovered QSOs? What was the first QSO discovered? To Maarten Schmidt (1963) goes the credit for realising that the emission lines he saw in a 13 mag star were the Balmer series in hydrogen at a redshift of 0.158. The first QSO had been recognised. But discovery is a complex process. Schmidt observed the ‘star’ because it was associated with a radio source 3C 273 by means of an accurate radio position. This was the first of several instances where accurate radio positions have enabled significant progress in the QSO story.

The carbon-rich proto-planetary nebula IRAS 22272 + 5435

view Abstract Citations (46) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Carbon-rich Proto--Planetary Nebula IRAS 22272+5435 Hrivnak, Bruce J. ; Kwok, Sun Abstract Ground-based photometry and spectroscopy is presented for IRAS 22272 + 5435, a 9th mag star with a large infrared excess. The flux distribution is 'double-peaked', with a visible and near-infrared component due to the reddened photosphere and a far-infrared component presumably due to a detached dust shell. About equal amounts of energy are detected from each. The spectrum is that of a peculiar G supergiant, Gp Ia. In addition, strong molecular bands of C3 and C2 are observed. The flux distribution is modeled and, together with published molecular-line radio observations, allows the determination of basic parameters of the central star and the dust shell. The source has the characteristics one would expect of a proto-planetary nebula, an object in transition from the asymptotic giant branch to the planetary nebula phase. Publication: The Astrophysical Journal Pub Date: April 1991 DOI: 10.1086/169928 Bibcode: 1991ApJ...371..631H Keywords: Infrared Sources (Astronomy); Planetary Nebulae; Protoplanets; Stellar Envelopes; Stellar Spectra; Astronomical Photometry; Astronomical Spectroscopy; Carbon; Infrared Astronomy Satellite; Astrophysics; INFRARED: SOURCES; NEBULAE: INDIVIDUAL ALPHANUMERIC: IRAS 22272; 5435; NEBULAE: PLANETARY; STARS: CIRCUMSTELLAR SHELLS full text sources ADS | data products SIMBAD (6)

A Catalogue of QSOs and Link Stars for the HST link of the Hipparcos Reference Frame

AbstractWe present a list of bright (< 17 mag) southern QSOs and bright (< 11 mag) stars that may be suitable for theHubble Space Telescopelink between theHipparcosastrometric reference frame and the VLBI extragalactic frame. The QSOs have been selected from various lists of radio objects and identifications. The stars have been selected from the Strasbourg (CDS) data base and from the Preliminary Second Cape Photographic Catalogue, and supplemented with stars measured from the SERC IIIa-J Schmidt survey. The list of QSOs and stars have been included in theHipparcosandHSTschedule of observations.

TIME-RESOLVED CCD PHOTOMETRY OF AN ENSEMBLE OF STARS

ABSTRACT A technique for obtaining CCD photometry of a large ensemble of stars, with precision limited by atmospheric scintillation and photon statistics is presented. Under bright-sky conditions with a 0.9-m telescope, a precision of about 0.0015 mag relative to an ensemble average standard was obtained for 12th-13th mag stars in M 67 with exposure times of 1 min. The increase in noise level due to variable cirrus clouds is minimal. Effective noise levels for the detection of coherent oscillations with periods of 5-20 min could thus be reduced to about 30 micromag over ten nights of observing for stars of this brightness. A much larger ensemble of faint stars could be followed at lower precision with sky background and photon statistics as dominant error sources. Four probable-cluster DA white dwarfs were detected in the old galactic cluster M 67, using B, V calibration photometry.

BI Crucis

BI Crucis is a 12 mag star whose optical spectrum is characterized by a red continuum and variable emission line spectrum (Allen 1974, Henize and Carlson 1980, Whitelock et al. 1983). In order to investigate its symbiotic character on 18 February 1983 we have obtained at the 1.5m ESO telescope a 59 Å/mm spectrogram of the 5700-6900 Å region. BI Cru displayed a very rich emission line spectrum with very strong Hα. and prominent HeI (5876 and 6678Å) lines. Several FeII lines are also present which appear optically thick (Figure 1). A few absorption features (NaI, 6269-84) of interstellar origin are present. However, we find no trace of TiO bands (or of neutral atoms) in spite of Allen’s (1974) finding, but in agreement with Whitelock et al. (1983). Allen (priv. comm.) remarks that in his spectrum there are slight ‘waves’ in the continuum that looked like TiO absorptions. Thus the symbiotic nature of BI Cru is mostly based on its long term IR variability (T≅280 d, Whitelock et al. 1983). They also found the first overtone vibration rotation band of CO at 2.3 μm in emission. The CO emission band was recently resolved by McGregor et al. (1987). This is the first observation of CO in emission in a symbiotic object. The red continuum is more probably a highly reddened hot continuum. We note that a weak continuum is present in the LWR IUE image taken in March 1981 (Fig.2). This spectrum also shows a few emission lines of Mgll and FeII. BI Cru is also a strong IRAS source. Following the model of Kenyon et al. (1986) for D-type symbiotics, the cool component of BI Cru could be reddened by circumstellar dust. A high resolution ESO CAT/CES red spectrum shows Hα doubled by a central absorption extending from −38 to −290 km/s with respect to the center of the emission line which suggests the presence of intermediate velocity winds like in other symbiotic stars.

Neutral hydrogen towards 3C 10, the remnant of Tycho's supernova

Aperture synthesis observations of neutral hydrogen towards the remnant of Tycho's supernova (AD 1572), 3C 10, have been made with the Cambridge Half-Mile Telescope. Details of the absorption features indicate that the distance of 3C 10 is in the range of 1.7–3.7 kpc. The neutral hydrogen in a cloud in the local arm has a spin temperature ∼80 K and an optical depth of order unity. Numerous arc and filamentary structures are seen in emission; some have been analyzed in terms of expanding shells. These are found to have H I masses between 500 M⊙ and |$2.8\times10^5M_\odot$|⁠, and H I kinetic energies between 3.5×1040 J and 6×1043 J. Stellar winds are proposed as energy sources for two of the arcs because three open clusters are near the center of curvature of one, and a bright star near the center of the other. An open cluster, three 9th mag stars and two CO clouds are seen to coincide with various minima in the H I emission. Two other CO clouds coincide with bright H I emission features, as does the small H II region S175.

CPD -48 deg 1577 - The brightest known cataclysmic variable

The discovery is reported of a V = 9.4 mag star which has the properties of a cataclysmic variable. Its UBV colors are similar to those of UX UMa, and its brightness fickers with an amplitude of the order of 0.1 mag. Larger brightness variations (0.5 mag) are found on a time scale of years. Its spectrum is characterized by extremely weak absorption lines of He I and He II, as well as extremely broad, shallow lines of H. A broad K line is very weakly present in absorption. Emission cores with a very slow decrement are seen in the H lines. From a comparison with the known properties of other cataclysmic variables, the distance, reddening, and mass exchange rate are estimated. The space density of cataclysmic variables is also estimated, since the original spectroscopic survey is complete to magnitude B = 10.0.

Identification of 4U 1849-31 with V1223 Sagittarii and discovery of optical pulsations

The X-ray source 4U 1849-31 is identified with the 13 mag star V1223 Sgr, on the basis of a precise HEAO 1 modulation collimator X-ray position uniquely selected by the Ariel-5 sky survey location. It is shown by optical spectroscopy and photometry that V1223 Sgr is a cataclysmic variable, displaying a photometric period of 13.2 min that is interpreted as being due to the rotation of a degenerate dwarf. The similarity of this system to H2252-035 is noted.

Radius of the VELA pulsar

Lasker (1976) has proposed to identify a B roughly equals 23.7 mag star as thermal radiation from the hot neutron star associated with the Vela pulsar. It is shown that this identification, if correct, together with existing X-ray surveys of the Vela supernova remnant, requires that the radius of this pulsar certainly exceed 45 km, and probably 95 km.

Interstellar Reddening in the North Galactic Polar Cap I. The Dependence on Distance from the Galactic Plane

AbstractInterstellar reddening within the North Galactic Polar Cap (b11 ≥ 60 °) is determined from published UBV photometry of 38 stars with spectral type earlier than A. The detailed discussion of line‐blanketing and effects of surface gravity reveals that the horizontal‐branch stars and the hot subdwarfs among the sample can be treated like ordinary main‐sequence stars of Population I as far as the determination of colour excesses is concerned. No reddening is detected for stars with distances from the galactic plane less than 250 pc. For larger distances the mean colour excess slowly rises and keeps constant at EB—V = 0.033 mag for stars beyond 1000 pc from the sun. The latter objects show a considerable scatter in the individual amounts of reddening.