X-Ray Observations of Stars: First Results from Rosat

At the time of writing (i.e., September 1991), the ROSAT all-sky survey has been completed and almost the entire sky has been scanned with an imaging X-ray telescope down to a limiting flux of approximately 2 10−13erg/s/cm2 in the pass band 0.1 — 2.0 keV; in regions of deeper exposures near the poles of the ecliptic considerably fainter flux limits have been achieved. While the processing and analysis of this huge body of data is still in progress and hence final results on the number of detected sources and their distribution in flux are not yet available, the total number of detected X-ray sources will be around 60 000. Preliminary results from optical identifications of selected fields show that about one quarter of the X-ray sources discovered at high galactic latitudes come from by comparison nearby stellar sources (Fleming 1991), while at lower galactic latitudes up to one half of the detected X-ray sources are of stellar origin; in areas occupied by star forming regions (for example, Orion) or open clusters (for example, Hyades or Pleiades) a large number of the detected X-ray sources can be identified with young stars, yielding up to 80 percent of the total source count as galactic stars. For the whole of the ROSAT all-sky survey we may therefore expect about one third of the total sources to be of stellar origin. The vast majority of these stellar X-ray sources is of coronal origin (i.e., late-type low mass stars). Only a relatively small number of stellar X-ray sources will be associated with early-type massive stars where the X-ray emission is thought to arise from instabilities in their radiatively driven winds or metal-poor degenerate stars where the X-ray emission comes from portions of the atmosphere considerably hotter than the optically visible photosphere. From the preliminary analyses performed so far it is already clear now that supersoft sources such as white dwarfs do not constitute a major fraction of the X-ray source population found in the ROSAT all-sky survey and the number of newly X-ray discovered white dwarfs will certainly be considerably less than one thousand. The X-ray emitting late-type stars are commonly referred to as ”active” stars, and the ROSAT all-sky survey catalog will comprise the most extensive list of such objects.

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Stars in the Rosat All-Sky Survey

Highlights of Astronomy ◽

10.1017/s1539299600008984 ◽

1992 ◽

Vol 9 ◽

pp. 235-239

Author(s):

J.H.M.M. Schmitt

Keyword(s):

White Dwarfs ◽

Open Clusters ◽

Source Population ◽

Late Type ◽

Low Mass Stars ◽

X Ray ◽

Star Forming ◽

Star Forming Regions ◽

Sky Survey ◽

Stellar Sources

The ROSAT all-sky survey has now been completed and the analysis of this huge body of data is in progress. While final results on the number of detected X-ray sources and their distribution in flux are not yet available, the total number of X-ray sources is expected to be around 60 000. Preliminary results from optical identifications of selected fields show that about one quarter of the X-ray sources discovered at high galactic latitudes come from by comparison nearby stellar sources (Fleming 1991), while at lower galactic latitudes up to one half of the detected X-ray sources are of stellar origin; in areas occupied by star forming regions (for example, Orion) or open clusters (for example, Hyades or Pleiades) a large number of the detected X-ray sources can be identified with young stars, yielding up to 80 percent of the total source count as galactic stars. For the whole of the ROSAT all-sky survey we may therefore expect about one third of the total sources to be of stellar origin. The vast majority of these stellar X-ray sources is of coronal origin (i.e., late-type low mass stars). Only a relatively small number of stellar X-ray sources will be associated with early-type massive stars where the X-ray emission is thought to arise from instabilities in their radiatively driven winds or metal-poor degenerate stars where the X-ray emission comes from portions of the atmosphere considerably hotter than the optically visible photosphere. From the preliminary analyses performed so far it is already clear now that supersoft sources such as white dwarfs do not constitute a major fraction of the X-ray source population found in the ROSAT all-sky survey and the number of newly X-ray discovered white dwarfs will certainly be considerably less than one thousand. The X-ray emitting late-type stars are commonly referred to as “active” stars, and the ROSAT all-sky survey catalog will comprise the most extensive list of such objects.

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X-Ray Coronae from Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900114329 ◽

1998 ◽

Vol 188 ◽

pp. 13-16

Author(s):

R. Pallavicini

Keyword(s):

Open Clusters ◽

Temperature Structure ◽

List Type ◽

Star Forming ◽

Spectroscopic Observations ◽

Star Forming Regions ◽

Complete Mapping ◽

Sky Survey ◽

Order Of Magnitude ◽

Age Range

A number of major advances in stellar coronal physics have occurred since 1990 mainly as a consequence of imaging observations by ROSAT and spectroscopic observations by ASCA. These can be summarised as follows: 1.an all-sky survey has been performed by ROSAT at a sensitivity of ~ 2 × 10−13 erg cm−2 s−1, complemented by pointed observations an order of magnitude deeper;2.complete mapping and deeper pointings have been obtained for virtually all open clusters closer than ~ 500 pc, and covering the age range from ~ 30 Myr to ~ 700 Myr;3.complete mapping and deeper paintings have been obtained for several Star Forming Regions (SFRs) covering the age range ~ 1 to ~ 10 Myr;4.spectroscopic observations of bright coronal sources have been obtained with EUVE and ASCA allowing the derivation of the temperature structure and elemental abundances.

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AM Herculis Binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900055868 ◽

1996 ◽

Vol 165 ◽

pp. 403-414 ◽

Cited By ~ 2

Author(s):

K. Beuermann

Keyword(s):

White Dwarf ◽

White Dwarfs ◽

Close Binaries ◽

Physical Processes ◽

X Ray ◽

Sky Survey

AM Herculis binaries contain mass accreting magnetic white dwarfs which appear as bright X-ray sources in the ROSAT All Sky Survey. About 52 systems are presently known which allow detailed studies of the evolution of magnetic close binaries and of fundamental plasma-physical processes in the accretion region on the white dwarf.

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Optical Identification of the ROSAT All-Sky Survey Sources in Two 2° × 2° Fields

International Astronomical Union Colloquium ◽

10.1017/s0252921100040653 ◽

1997 ◽

Vol 159 ◽

pp. 427-428

Author(s):

Y. Zhao ◽

J. Zhong ◽

J. Wei ◽

J. Hu ◽

Q. Li

Keyword(s):

Ccd Camera ◽

Seyfert Galaxies ◽

Astronomical Observatory ◽

Active Galaxies ◽

Clusters Of Galaxies ◽

Late Type ◽

Optical Identification ◽

X Ray ◽

Sky Survey

AbstractWe used the CCD camera and spectrograph of the 2.16-m telescope of Beijing Astronomical Observatory to identify the ROSAT All-Sky survey sources in two 2° Ü 2° fields. Of a total of 16 X-ray sources, we identified 13 of them as follows: two QSOs, two Seyfert galaxies, two active galaxies, two clusters of galaxies, and five late-type stars. Three X-ray sources remained unidentified.

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Redshift measurement through star formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833046 ◽

2019 ◽

Vol 629 ◽

pp. A7

Author(s):

Mikkel O. Lindholmer ◽

Kevin A. Pimbblet

Keyword(s):

Star Formation ◽

Galaxy Clusters ◽

Main Sequence ◽

Formation Rate ◽

Sloan Digital Sky Survey ◽

X Ray ◽

Star Forming ◽

Sky Survey ◽

The Galaxy ◽

Galaxy Population

In this work we use the property that, on average, star formation rate increases with redshift for objects with the same mass – the so called galaxy main sequence – to measure the redshift of galaxy clusters. We use the fact that the general galaxy population forms both a quenched and a star-forming sequence, and we locate these ridges in the SFR–M⋆ plane with galaxies taken from the Sloan Digital Sky Survey in discrete redshift bins. We fitted the evolution of the galaxy main sequence with redshift using a new method and then subsequently apply our method to a suite of X-ray selected galaxy clusters in an attempt to create a new distance measurement to clusters based on their galaxy main sequence. We demonstrate that although it is possible in several galaxy clusters to measure the main sequences, the derived distance and redshift from our galaxy main sequence fitting technique has an accuracy of σz = ±0.017 ⋅ (z + 1) and is only accurate up to z ≈ 0.2.

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X-ray Flare Rate of T Tauri Stars in Taurus

International Astronomical Union Colloquium ◽

10.1017/s0252921100035028 ◽

1995 ◽

Vol 151 ◽

pp. 216-217

Author(s):

R. Neuhäuser ◽

Th. Preibisch

Keyword(s):

Star Formation ◽

Main Sequence ◽

T Tauri Stars ◽

Medium Size ◽

Late Type ◽

Large Sample ◽

X Ray ◽

T Tauri ◽

Sky Survey ◽

Low Mass

AbstractWe study the X-ray emission of several hundred (young, low-mass, late-type, pre-main sequence) T Tauri stars (TTS) in the Taurus T association, a nearby well-studied region of ongoing star formation. We report on X-ray emission variability of TTS as observed with the flux-limited ROSAT All-Sky Survey (RASS). Since RASS observations are spatially unbiased, we can investigate the X-ray flare rate of TTS on a large sample. We find that large flares are very rare (once per year), while medium-size flares can occur once in ∼ 40 days.

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Revealing the “missing” low-mass stars in the S254-S258 star forming region by deep X-ray imaging

Astronomy and Astrophysics ◽

10.1051/0004-6361/201117074 ◽

2011 ◽

Vol 533 ◽

pp. A121 ◽

Cited By ~ 11

Author(s):

P. Mucciarelli ◽

T. Preibisch ◽

H. Zinnecker

Keyword(s):

Low Mass Stars ◽

X Ray ◽

Star Forming ◽

X Ray Imaging ◽

Low Mass

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X-ray source population in the polar ring galaxy NGC 660 as observed by Chandra

Research in Astronomy and Astrophysics ◽

10.1088/1674-4527/21/11/289 ◽

2021 ◽

Vol 21 (11) ◽

pp. 289

Author(s):

Nurnabilah Nazri ◽

Adlyka Annuar

Keyword(s):

Threshold Value ◽

Population Based ◽

Source Spectrum ◽

Source Population ◽

Ratio Distribution ◽

X Ray ◽

Star Forming ◽

Polar Ring ◽

The Galaxy ◽

Ring Galaxies

Abstract We present Chandra observations of the nearby polar ring galaxy NGC 660 to study its X-ray source population. Based on our analysis, we detected a total of 23 X-ray sources in the 0.5−8 keV band, with luminosities ranging from ∼1037 to ∼1039 erg s−1. Twenty-two of these sources are located off-nuclear and have luminosities below the ultraluminous X-ray source (ULX) threshold value of L 0.5−8 keV < 1039 erg s−1, suggesting that they are likely to be X-ray binary (XRB) candidates. The remaining source is located at the center of the galaxy, suggesting it is an active galactic nucleus (AGN). However, we estimated that four of the detected sources could be associated with background objects. Based on the source count rates in each of the Chandra observations, we found evidence for variability in nine of the 23 sources, including the AGN. However, further investigation with spectral analysis suggested no significant differences in the AGN luminosities between the observations. The X-ray luminosity distribution of the galaxy was found to be generally lower than that expected from previous studies on star forming and collisional ring galaxies. No ULX was also detected in the galaxy, in contrast with what was expected from the galaxyʼs SFR and metallicity (i.e., SFR = 14.43 ± 0.19 M ⊙ yr−1 and Z = 0.94 ± 0.01 Z ⊙, respectively). These results suggest a deficit in the X-ray sources detected. Based on source hardness ratio distribution, we found evidence that the fainter sources have a harder source spectrum, indicating higher absorption. This further suggests that there could be more X-ray sources that were not detected in the galaxy due to significant obscuration.

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Deep GMRT 610 MHz observations of the ELAIS N1 field: catalogue and source counts

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2954 ◽

2019 ◽

Vol 491 (1) ◽

pp. 1127-1145 ◽

Cited By ~ 6

Author(s):

E F Ocran ◽

A R Taylor ◽

M Vaccari ◽

C H Ishwara-Chandra ◽

I Prandoni

Keyword(s):

Spectral Index ◽

Low Frequency ◽

Source Population ◽

X Ray ◽

Star Forming ◽

Density Distributions ◽

Deep Image ◽

Frequency Source ◽

Minimum Noise ◽

Good Agreement

ABSTRACT This is the first of a series of papers based on sensitive 610 MHz observations of the ELAIS N1 field, using the Giant Metrewave Radio Telescope. We describe the observations, processing and source catalogue extraction from a deep image with area of 1.86 deg2 and minimum noise of ∼7.1 μJy beam−1. We compile a catalogue of 4290 sources with flux densities in the range of 28.9 μJy– 0.503 Jy and derive the Euclidean-normalized differential source counts for sources with flux densities brighter than $\rm {35.5\, \mu Jy}$. Our counts show a flattening at 610 MHz flux densities below 1 mJy. Below the break the counts are higher than previous observations at this frequency, but generally consistent with recent models of the low-frequency source population. The radio catalogue is cross-matched against multiwavelength data leading to identifications for 92 per cent and reliable redshifts for 72 per cent of our sample, with 19 per cent of the redshifts based on spectroscopy. For the sources with redshifts, we use radio and X-ray luminosity, optical spectroscopy and mid-infrared colours to search for evidence of the presence of an active galactic nucleus (AGN). We compare our identifications to predictions of the flux density distributions of star-forming galaxies (SFGs) and AGN, and find a good agreement assuming the majority of the sources without redshifts are SFGs. We derive spectral index distributions for a sub-sample. The majority of the sources are steep spectra, with a median spectral index that steepens with frequency: $\mathrm{\alpha ^{610}_{325}\, =\, -0.80\, \pm \, 0.29}$, $\mathrm{\alpha ^{610}_{1400}\, =\, -0.83\, \pm \, 0.31}$, and $\mathrm{\alpha ^{610}_{5000}\, =\, -1.12\, \pm \, 0.15}$.

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