# Typography: general typing rules

Fine tuning of the textThe following should be used to improve the readability of the text:

\, | a thin space, e.g. between thousands in numbers with more than 4 digits; a line division will not be made following this space, |

-- | en-dash; two hyphens, without a space at either end, |

-- | Please note: in TEX, -- gives an em-dash
"--"; we do not use this, but rather
the shorter en-dash with spaces, i.e. space,
two hyphens, for an en-dash, space, to give an
"em-dash". |

- | hyphen; no space at either end, |

$-$ | minus, in the text only, |

~ | fixed space, e.g. between parts of names. |

Their use is best explained in the following example.

20\,000 km, 1\,000\,000 s, HD 174\,638 1950--1985, p.~11--21 this -- written on a computer -- is now printed signal-to-noise ratio, early-type, metal-poor, non-relativistic $-30$~K, $-5\ ^{\circ}$C Dr.~h.c.~Rockefeller-Smith and Prof.~Dr.~Mallory

Sample output:

20000 km, 1000000 s, NGC 468324 1950-1985, p. 11-21 this - written
on a computer - is now printed signal-to-noise ratio, early-type, metal-poor,
non-relativistic -30 K,
-5 °C Dr. h.c. Rockefeller-Smith and
Prof. Dr. Mallory

Units, symbols, and nomenclature

Authors can considerably help the publisher by observing the following rules:

Special typefaces
- The text should make clear distinctions between physical variables, mathematical symbols, units of measurement, abbreviations, chemical formulae,
- Italics and boldface should be used appropriately to identify physical or mathematical variables. In general, variables are set in regular italics, vectors in boldface italics. Physical constants such as the speed of light, the Boltzmann constant, the Hubble constant and the solar mass are also set in regular italics.
- Italics should never be used for units of measurement e.g. km, erg
cm
^{-2}, s^{-1}or for chemical formulae unless, of course, these items fall within a passage that is entirely in italics. - As far as possible, italics should be avoided for the following: mathematical signs such as "d" (total differential), "e" (base of natural logarithm), "i" (imaginary unit), "pi" (3.14159...), and abbreviations used as subscripts or superscripts to variables, but serving merely as labels, e.g. (d = dust), (e = electron). However, in conformity with the rest of the text, italics should be used if the subscripts or superscripts are variables themselves.
- For common units of measurement (SI and non-SI), standard abbreviations
should be used. Unusual units may, at the authors' discretion, be written in
full, at least at the first mention. Some traditional, non-SI units persist in
astronomy literature. Some are acceptable (e.g. erg, angström/Å) but
others are obsolescent and should be avoided (e.g. micron/). Compound
units in which the meaning "per" is implied can be written using either a
slash or a negative index: A&A prefers the latter style, e.g. km s
^{-1}instead of km/s. - For the correct naming of astronomical objects outside the solar system, it is suggested that authors refer to the recommendations on nomenclature given by the International Astronomical Union at http://cdsweb.u-strasbg.fr/Dic/how.htx .

**Emphasize:**- (\emph{Emphasize}) should be used for emphasis in the text.

**Vectors:**- \vec{Symbol},
vectors may only appear in math mode.

Input examples:

$\vec{A} \times \vec{B} \cdot \vec{C}$

- $\vec{A\/}^{\rm T} \otimes \vec{B} \otimes \vec{\hat D}$

**Tensors:**- \tens{Symbol}],
tensors may only appear in math mode.

Input example:

\tens{ABC}

**Ions:**- \ion{<element symbol>}{<degree of ionization>},
the degree of ionization in the \ion command has to be given as lower
case roman numerals (e.g. \ion{H}{ii}
which yields H II).

Input examples:

\ion{H}{II}

- \element[ ][13]{C}

**Elements:**- \element[<electrical charge>][<number of nucleons>]
[<number of protons>]

[<number of neutrons>]{<element symbol>}

Note, that if you want to have for example^{13}C, the last two optional arguments may be omitted: \element[ ][13]{C}.

Signs and characters

You may need to use special signs. The available ones are listed in different
books (*LaTeX User's Guide & Reference Manual, The LaTeX
Companion, etc.*). We have created further common astronomy symbols:

In | Explanation | Out | In | Explanation | Out |

\sun | sun symbol | \fs | fraction of second | ||

\degr | degree | \fdg | fraction of degree | ||

\diameter | diameter | Ø | \fp | fraction of period | |

\farcs | fraction of arcsecond | ||||

\fd | fraction of day | \farcm | fraction of arcmin | ||

\arcsec | arcsecond | \fh | fraction of hour | ||

\arcmin | arcminute | \fm | fraction of minute |

In | Out | In | Out |

\la | \ga | ||

\cor | \sol | ||

\sog | \lse | ||

\gse | \grole | ||

\leogr | \loa | ||

\goa | \getsto | ||

\lid | \gid |

## Mathematical formulae

All equations that you are referring to with \ref must have the
corresponding \label - please use this mechanism only. Punctuate a
displayed equation in the same way as ordinary text.

\left( \left[ |

\right) \right] |

Note that the sizes of the parentheses or other delimiter symbols used in
equations should ideally match the height of the formulas being enclosed. This
is automatically taken care of by these LaTeX commands.

**Italic and roman type in the math mode**

In math mode LaTeX treats all letters as though they were mathematical or
physical variables; hence they are typeset in italics. However, any textual
elements within formulas should be set in roman. Roman should also be used for
subscripts and superscripts

*in formulas*where these are merely labels and not in themselves variables, e.g.$T_\mathrm{eff} = | ||

5\times 10^{9}\ \mathrm{K}$ | produces | |

$T_\mathrm{K}$ | produces |
T_{K} (K = Kelvin) |

$m_\mathrm{e}$ | produces |
m_{e} (e = electron) |

However, do not use roman if the subscripts or superscripts represent
variables, e.g.
.
Please ensure that

*physical units*(e.g. pc, erg s^{-1}K, cm^{-3}, W m^{-2}Hz^{-1}, m kg s^{-2}A^{-2}) and*abbreviations*such as Ord, Var, GL, SL, sgn, const. are always set in roman type with an appropriate inter-word spacing. To ensure this, use the \mbox command: \mbox{Hz}.
On p. 44 of the

*LaTeX User's Guide & Reference Manual*(2nd ed.) by Leslie Lamport, you will find the names of common mathematical functions, such as log, sin, exp, max, and sup. These should be coded as \log, \sin, \exp, \max, \sup and will then automatically appear in roman.
In order to distinguish "d" used as the "differential sign" and "e" used
as the "exponential function" from normal variables, set these letters in
roman.
Chemical symbols and formulas should be set in roman, e.g. Fe not

*Fe*, H_{2}O not*H*, H not_{2}O*H*.